I use FCP, which means I have to Log & Transfer the P2 clips to MOV files. This obviously adds some time to the process, but it is a workflow I am comfortable with. But I always retain the original MXF files stored separately. Your question implies there is some disadvantage to converting, but there is no loss of quality, just more files on the hdd.
In FCP there's an import to QuickTime for P2 footage. Which can be avoided if you get Raylight, Calibrated, MXF4Mac, etc. Personally I use log and transfer as I rarely do a job where I need to exchange MXFs.
I use Log and Transfer too. Because not only does it stitch together spanned clips, but I can name them what I want, mark IN and OUT and use only what I need (although I always import full clips), and if your drive fails, all you have to do is hit BATCH CAPTURE and FCP imports all the footage again.
I NEVER work with the originals. Some people do...that is a viable workflow (news)...but I don't. And people who complain about the transfer time, well...if you wanted to work off the original MXF files, you SHOULD copy them to your media drive anyway, and archive the masters. This copying process takes time too...about as much time as Log and Transfer takes.
But, lately I have gotten P2 footage with a lot of embedded metadata that I need to access. In this case, I use HDLog to create alias' that I can then import into FCP with all that metadata imported into FCP columns.
There are MANY different workflows for P2...that's what makes it so cool.