Another issue is re-knitting. While knitting I continuously improve the piece in my head. Often those thoughts about ways how this or that could have been done better become impossible to ignore. The only option then is to frog back and knit from the start (or middle if I'm lucky).
I ripped back about 15cm of the dress knitted in the round (5 yr size) only because I thought ssk would look nicer than k2tog tbl. That part looks as this now instead of zig zag k2tog tbl would create.
I often knit and sort of design as I go along. Sometimes (if not always) I have knitted pretty large piece until I realized I had to do something different (usually at the very beginning). For this top I knitted, ripped back and re-knitted again cabled yoke part several times until got cable allocation and proportions as I wanted.
I knitted hood for this cardigan once and was not satisfied how increases in side parts turned out. At first I had done them symmetrically and in the centre of hood side sections. Ripped back and started again with increase lines allocated closer to the outer part on the each side of the hood. Then to finish hood with sideways knitted edge I had to do it three times until it looked smooth enough. Too many slipped and knitted together stitches and too many techniques to choose from. I guess I could have knitted another cardigan in the time I devoted to hood improvements :)