The obvious advantage is that it's quite likely that they'll be well rounded, knows different stuff and got lots of experience in the world, there are tons of great skills especially found in founders.
At the same time the chances are he/she will be leaving the company after 9 months, because she just discovered "the next best thing" and want to work on that because she saved some money in the last 9 months. I try to talk the person and understand what's the long term plan, whether they are actually committed or just want to take a breath and get financially better in between projects.