Taking profits at the right time is good, but I think for some quality altcoins with use-case are good to hold in the long-term.
The problem here is the picking of those projects with use cases. Not much have these and even major coin listed are just traded without any use case. Take for example Binance. Not all tokens there have use cases. They say Binance listed only good one but I doubt that all of them are good. Some are just laid to get listed so better avoid trusting all altcoins listed not every project is good.