It seems that it is smart that as you sell the altcoins when the market rise back 20% or more, and buy back when the market drops back.
But it will let you loss the big waves like in 2017, from 2014 to early of 2017, the market shacks all the times, but it boomed in 2017, if you do as above, you will leave the boat, and can't join back.
This depends on the situation at the same time to your knowledge. The situation is not that stable therefore you need to hold it when the market is down then sell at high price, that is the cycle that professionals are dealing with. When it comes to the knowledge, you need to analyze the market in when to let go and hold. Everything has a perfect timing, you need to be wise.