Pros: You know you are 'in' and can relax the rest of the year, cancel some interviews, save money, etc.
Cons: You often have to pay your deposit before you even interview at other schools, so you could end up getting in somewhere you like more and lose that deposit.
Neutral: Keep in mind that if you are a competitive applicant, there isn't much of an advantage to special 'early' interviewing, as long as you aren't slacking and returning your secondaries in October.
And now a tangential anecdote:
I ended up going to Western after a very early acceptance a couple of years ago. At the time I was mainly interested in location, and Western has the Northwest Track which allows me to return to the NW this spring for rotations. I ended up cancelling interviews at CCOM, Touro, MSUCOM, and a bunch of MD schools.
Now I wish I had not been so attached to geography, because there were a lot of great schools I had a shot at. Not that Western has been bad, but its no CCOM, and as I go through this process my interest in getting a strong education is starting to outweigh my desire to be in any specific place.
On the bright side, I know I won't be making the same mistake with residency