It's habit and I use a leader now at the start of everything (even if I'm doing a rare garment project), except if I'm sewing two strips together of uneven length, then I'll start on the long end of the bottom piece.
I chain everything I can as much as possible, and start with those leaders for the last 10 years because I feel it does help my accuracy -- some people also use enders but that hasn't been so much of an issue for me. Strips or pieces into sub-units, sub-units into blocks, blocks into rows... I prefer to do all of one set at a time, that is, if I have to make 1000 HST, I make all of them before moving on to the next step. It gives me consistency which is a good thing -- but not if I make 1000 mistakes. Then you learn to correct those or turn them into something "not so planned". With scrappier projects I can't always do that but I try to at least do 4 sets of things at a time.
Keep in mind when you are sub-cutting strips that your stitch size should be on the small size so that too much doesn't come apart when you cut it.