Capturing the source of your creation is the most important part of the transduction process.
Recording can be "live", "track by track" or a mix of the two. Sometimes you only need to add a track to previously recorded material, in which case we record the new audio and mix it back in to the original. In other cases, we're starting from scratch with preproduction sessions where the material is rehearsed for a short period of time with some throw-away recording, just to refresh. Once we're refreshed on our material, we plan the flow of the session and then begin. Sometimes, preproduction isn't necessary at all! Artists can come in and start recording immediately. My shortest session was 35 minutes and only 1 take.
There are some price/quality trade offs when choosing your recording plan:
Sometimes artists look for a particular 'live' sound or 'room' sound in which the recording aspect becomes part of the creative process. This can also be expensive if not planned for or too much experimentation drains the clock. Its wise to bring a few reference records to your engineer so they can cut out a lot of guess work.