What does an ensemble cast bring to a movie?

In the wake of Tinker, Tailor and with Contagion and the terrifyingly star-filled New Year's Eve on the way, we ask what ensemble casts add to movies

To generalise for a moment, ensemble casts are more often seen in television shows than on the big screen. Having a number of characters who hold equal status or importance to the ongoing narrative is a format upon which 20-something-episode seasons of a show can be sustained, but isn't quite so effective in the finite time-scale of a movie.
Nevertheless, filmmakers like Quentin Tarantino, Steven Soderbergh and Edgar Wright have consistently deployed ensemble casts in their movies, with Soderbergh having notably gotten a whole Ocean's trilogy out of one big, starry ensemble.

Essentially, there are two types of ensemble movie. You can either tell a single story in which every character is played by a good or at least recognisable actor, or go down the increasingly prolific route of showing a number of interweaving narratives populated by stars given equal stature, a method of storytelling that is closer to the complexities of popular television.

Soderbergh seems to have done both, with the release of his upcoming thriller Contagion. The film stars Matt Damon as a man who loses his wife, Gwyneth Paltrow, to a pandemic. Elsewhere, Lawrence Fishburne and Kate Winslet are health authorities who are trying to cure the disease, while Jude Law, Marion Cotillard, John Hawkes and Bryan Cranston all play their own wipe-clean antibacterial parts in the infection paranoia movie.
Contagion seems to have interweaving plotlines galore, whereas the Ocean's movies each go down the more focused story route of a heist thriller. Arguably, only Ocean's Eleven manages to find something for each of the crew-members to do. As a remake of a Rat Pack flick, it was always going to be an ensemble piece. The sequels struggle to manage the increasingly large cast, which is not an uncommon problem.

The worst of this more starry variety is the ensemble romantic comedy. Currently playing in cinemas is the trailer for New Year's Eve, a spiritual sequel to Valentine's Day. Given how the earlier film was an insipid cross between Robert Altman's Short Cuts and one of those 15-word crossword puzzle tie-breakers that starts “Love is...”, you can't expect too much from New Year's Eve.
And yet it's tempted Ashton Kutcher and Jessica Biel back into the fray, and picked up new cast-members in the form of (deep breath) Robert De Niro, Michelle Pfeiffer, Josh Duhamel, Jon Bon Jovi, Zac Efron, Lea Michele, Carla Gugino, Katherine Heigl, Ludacris, Seth Meyers, Sienna Miller, Sarah Jessica Parker, Abigail Breslin, Til Schweiger Hilary Swank, Sofía Vergara and Halle Berry. Phew.

Somehow, the budget on these films doesn't rocket through the roof for all of the celebrity pay-packets that need to be handed out, and Valentine's Day ended up doing pretty well at the box office, despite being so sugary audiences were at risk of falling into diabetic comas. With the approach of casting everyone who's free and famous, you're bound to appeal to someone, so if there's one thing a starry ensemble brings to a film, it's diverse audience appeal.

But a recent exception to the general rubbishness of romantic ensemble movies is Crazy, Stupid, Love, which stars Steve Carell, Ryan Gosling, Julianne Moore, Emma Stone, Kevin Bacon and Marisa Tomei. They're all good actors, in a film that doesn't boil down complex adult relationships to screwball antics and miscommunication. It’s a film which doesn't trade on the star quality of the actors alone.
That's for the marketing to do. It helps enormously that all of the principal cast are very talented, and play likeable characters we can root for, but it also brings all of those characters together in a way that doesn't involve repetitive and irrelevant vignettes.

The elephant in the room is Tinker Tailor Soldier Spy, which is the most obvious recent example of an ensemble cast bringing the best calibre to a film. Gary Oldman, Colin Firth, John Hurt, Mark Strong, Benedict Cumberbatch, Tom Hardy, Toby Jones and Ciarán Hinds all play their parts in the film's sprawling espionage narrative, but the triumph of Tinker as an ensemble film is in how well they all operate together.
Between this and the final Harry Potter films, most of the big British actors currently working seem to have been employed for the last two years or so. George Smiley is a bonafide, name-above-the-title leading man role for Gary Oldman, after seeing him in supporting roles as Sirius Black, and also as Commissioner Gordon in Christopher Nolan's Batman movies.

That's more of a benefit to the actor than to an ensemble film itself, but it sets up a model whereby actors can supplement big roles in passion projects with smaller roles in big-budget prestige films. I'm not certain of what Robert De Niro is playing at, appearing in New Year's Eve, but if we actually see him doing some genuinely good work in the next 12 months or so, there's your answer.
So to conclude, although the ensemble cast has been appropriated by romantic comedies that just wind up confused, there's still some prestige to the ensemble cast, if deployed correctly. Even Crazy, Stupid, Love has shown us that rom-coms can reap the benefits of an established cast without falling back on star appeal and nothing else.
As seen in Tinker Tailor Soldier Spy, it allows for a film in which every single role is played by someone brilliant. In that film each star is on an equal footing, to some extent, and it allows the audience to focus on the story without being distracted by showy performances. Not all ensemble films can be so finely balanced, but as star vehicles are generally selling fewer tickets individually, you can expect to see them clubbing together even more in the future.