I once shipped a crud app a few weeks earlier than I wanted to because of pressure from managers. I warned them that I hadn't done any optimizations, and it would quickly become unusable with real world use. So naturally, as soon as it was deployed I was reassigned to another project. 3 weeks later the users were complaining it was slow, in 6 weeks it was taking 20 minutes to load. They finally agreed to let me optimize it, in an hour I had it to 5 minutes, in a week I had it loading in 10 seconds. I could get it faster, but I was reassigned again, and at this point it is plenty fast for the users in question.

If I had done the easy change to get it to 5 minute before deploying, it would likely still be that way today annoying my users, but not enough to justify changing.