As well as the distribution and promotional side they also manage aspects of music such as trademarks and copyright, scouting and developing new artists, maintaining contact with artists and band managers who they offer contracts to based on their current or potential popularity.
In an extremely saturated market of music where practically every base and avenue has already been covered, many artists currently rely very heavily on record labels to begin their path to success and even be noticed in the first place. This could involve giving them positive media reports, promote tours, market their merchandise and getting the actual product available in digital and physical format.
Rough Trade are an example of an independent label but one in this case indie doesn't necessarily mean small. Some of their most successful artists have been alternative, mostly British indie/post punk bands who have become huge, most namedly ones like the Smiths, the Libertines, Arcade Fire and the Strokes; achieving a mixture of huge cult and commercial success, eg the latter two having headlined Reading Festival in 2010 and 2011, respectively. They field a mixture of alternative artists but these are the type I associate most strongly with the label even before researching into it, which perhaps indicates the areas in which they have achieved success.
The label is owned by Beggars Group, who own other independent labels such as 4AD and Matador Records and XL Recordings. 4AD is less active now, having its heyday in the 1980s and 90s, Matador fields generally smaller bands and XL features a small number of often very popular artists from a range of genres, such as Dizzee Rascal, The Prodigy, The White Stripes, Radiohead, and Adele. The group all originated from London with the Beggars Banquet record stores, originating in Earl's Court in the 1970s.
Warner Bros Records is older and larger, stemming from the huge worldwide multimedia corporation that began with the film company in California at the start of the 20th century and merged into TimeWarner in 1989 in a deal worth $14bn. Today they are signed with some of the world's biggest music artists such as the Red Hot Chili Peppers, Green Day, Biffy Clyro, Avenged Sevenfold, tending to have a main focus on broad appeal alternative and rock artists. They do not only take on the most enormous established artists but also take on those they believe to have popular potential such as Royal Blood. The label is widely known as one of the 'Big Four' labels amongst Sony, Universal, and EMI groups, which apart from EMI are also multimedia conglomerate umbrella corporations.
Because these main four label groups own so many other labels and other parts of the media, most labels outside their ownership are often considered independent.
Many established artists create their own record labels so they can avoid larger proportions of their profits going to a label, and also to help upcoming artists in their genres. This is most common in the hip-hop genre with artists such as Jay Z and Kanye West.