Technically on Wifi the fastest possible speed you can have is 54 Mbps since that is the max transmission speed of 802.11g which is what the Droid has.
I also jump on Wifi to remote desktop into my computer at work while I am in the office sometimes or even to remote into my server while I am at home.
While it's true that you can theoretically get up to 54Mbps over Wifi, you won't see that in practice, and no matter how fast your connection to the WiFi Access Point is, Internet speeds are generally much slower so that will be your bottleneck.
The main advantage would be the faster connection. My wifi connection at home runs about three times faster than 3G. Also there is a 5GB limit on data per month, so there are some folks that use their wifi to keep under that limit.