This totally depends on what type of coin you're holding and whats your estimated investment time frame. If you will be comfortable holding your coins (mostly bitcoin) for as long as it takes to make a profit then, you can by into this idea of not selling your coins at lost but if you're not a hodler taking small losses aren't a bad idea to avoid further losses.

A related example are those who sold their bitcoin at (lets say) around $14000 after the sudden bitcoin dropped from the highest ATH. If those set of individuals were privilege to rebuy around the $3500-$5000 price range or current bitcoin price. You can consider such loss a good loss as it gave you an opportunity to gain more bitcoin. So If you're not a long term investor, the idea if not selling at lost shouldn't be a stretagy you live by.  Choose what best works for you.