If regrets about yesterday's decisions and actions help you do better work today, then they've served a useful purpose.
"I wish I'd taken that job."
"I should have been more careful before I shipped that out the door."
"I could have been more kind."
"I'll do better next time."
Most of the time, though, we use regrets to keep us from moving forward. They paralyze us in the face of possibility. We don't want to do something if it reminds us of that black hole we have in our past.
It's useful if you can forgive yourself, because the regrets you're carrying around are keeping you from holding onto the possibility that you can contribute even more tomorrow.