Fit-to-Fill is 4-point edit. It will put source IN to master IN and source OUT to master OUT adjusting source speed.
Replace is a great tool. That’s how I sync dailies working on features. Park on a clap in the sound take in the viewer, park on a frame where sticks hit in the timeline, Replace, next. That’s how I change one take for another in an edited scene. That’s what I often use instead of slip cutting to music.