Reading in the manuals as I prep for a new project, there are three workflows, the first is the best of them:
Capture and work in native HDV (how final cut pro is designed to be used) and do all effects work in pro res 422 including color correction etc. Basically any effect you do will automatically boot you to pro res 422 UNLESS
You choose to keep footage in native HDV when you apply effects (not a wise choice as it chews up processor time and it is likely that you’ll get better results with pro res 422 as it should hold up better for effects) However, if you are going right back out to HDV tape, then this option is a good choice.
The other option is to capture in the Apple Intermediate Codec and all work (including effects) is done in this codec, but file sizes are HUGE. But this is much less processor intensive — so if you have an older machine with lots of hard drive space, probably the way to go.