i havent used my backup, but looking at it on appbrain, it looks like it just backs up copies of most of the data on your phone. bootstrap allows you to reboot into recovery, where you can create a nandroid backup, which is basically a snapshot of your device at the time of the backup, allowing you restore to that point at any time (similar to a system restore on windows).
if you plan on flashing roms/themes, nandroids are pretty essential. they allow you to fix any problems that might arise from a new rom by flashing back to a point before you installed it.
my backup looks handy enough, but one question i would have is that when backing up apps, does it also backup the market link (as titanium does)?