you should only use bitcoin as your primary cryptocurrency and if you are interested in any altcoin just try trading them. never invest in any of them since they are all failing one after another no matter what their name is.
I agree keeping BTC as main crypto currency. But those who understand the altcoin market can make good money, if you dont understand it the opposite is true you can lose a lot.
I don't think it's a bad thing holding a few altcoin's but I consider them more of a gamble. Reason it's a gamble is all the pump/dump stuff. If you know what your doing it is better then gambling, but I won't pretend I'm a master at altcoin trading.
There are some that can do it and profit. And even some who are able to program bot's with good settings that make money all day, personally I'm blown away by people who can do this especially those who figure out the parameters of bots.