I think it depends on the altcoins that you are holding. If the altcoin your holding is not good you can sell it all and buy bitcoin. But if your altcoin have so much potential yo be good keep holding them.
That is true. Holding a bad altcoin causes a lot of things. We have to determine which coins should be held and should not be held. Instead of holding a bad coins like that, we can make our own research in order to find out which coins are good for us and which are not. AS you can see, there are many good coins on the market cap such as ethereum or litecoin. Therefore, if you realize that your coins are bad, there is no point in holding anymore. You should sell it and buy other coins which are better