Generally opt-in when thinking weather to decide on a large scale changes.
For important decisions (e.g. quitting a job or ending a relationship), those who make a change report being substantially happier two months and six months later. From a large-scale randomized field experiment in which research subjects having difficulty making a decision flipped a coin to help determine their choice. Heads or Tails: The Impact of a Coin Toss on Major Life Decisions linked from
Whenever I start to make substantive changes to my design file I "fork" my designs. I duplicate a file to save a previous state. It turns out that I rarely come back to the previous states of the project. Substantive changes in most cases are bringing quality.