imo, it depends on how you see trading. If you're a gambler, rolling the dice, why set limits? If you see it as a business, then decide your entry/exits by how much you want to make/lose. I think the Waltons(Walmart) used to set a profit limit of 12-15% / item and became the wealthiest family in the country. I see trading the same way, I only need singles/doubles to make a solid living and survive - in this business most fail, some breakeven and a tiny percent actually make a living. Win/loss is great but breakeven is key. I'd rather exit at flat and re-enter then have a bigger loss and hope the market comes back.
Obviously, IV, plays a part, transaction size and if I'm up or down for the day is a part. Its different for everyone as risk is a question of perception.
But to answer directly, usually when any part of the transaction is up/down in $50-100 range I start scaling out to reduce my exposure. Sure, i pay more in commissions, but thats a limited loss unlike folks who hold on and hope the market goes their way but end up with big losses.
I also only trade less than five names and a few futures where I know how its works. I think folks who scan thousands of names and have a watch list of a few hundred names forget that major banks/dealers have teams of folks watching small groups of companies, so I'm not sure how one person can be familiar with a few hundred names and trade them successfully when major companies don't even try to do that. This isnt a swipe at anyone just a comment about my lack of understanding of that practice.
Anyways, good luck trading and its always curious how risk management threads just die out unlike MA threads which get hundreds and hundreds of comments resulting in massive threads. Maybe that shows that folks are more interested in rolling the dice than managing risk. i dunno.