Yeah, there are a couple benefits:

• what if you plan to vote on a certain day, but then there's a problem like illness, car breaks down, work or family emergency, etc. If you were planning to vote early, you still have a chance.
• if people try to suppress the vote, it's harder because they'd have to do so over several Early Voting days and there'd be more chance to counter them
• it puts less pressure on the system and increases throughput. Sometimes machines just break down normally, or there are supply shortages, and if it's the last day then you might have people waiting in line for hours.
• Finally I think from a campaign perspective, you're more likely to tell your friends that you voted early and suggest they do the same (or even that you contact the campaign and get involved somehow)