Does using the source window to set in and out points make any difference to how much work Prem Pro is doing or is it just an individual's workflow preference?
Does it make a difference to the performance if I import a 100 minute video and cut it into 100 one minte sections or import 100 videos pre-cut into one minute sections? Would one way be more work for Prem Pro?
To the first qustion - setting lots of in and out points should not have a significant impact to how much processor demand is put on teh Premiere file. Things that would make more of a difference is addition of many effects on the video.
To the second question, what are you doing with the video clips? If you are putting 2 one minute video clips together, that may be less processing than in you cut the multipe 1 minute segments and then put them together. It may not be significant though. It would also depend on the compression on the video and when you export, if you are making substantial changes to the format (like resizing, different compression settings).