No there aren't any disadvantages except your altcoin might be one of the ones that is beat up more than others in which case it might be fine to hold - it all depends on the scale of its fall and if there is any sizable support nearby. You don't want to fall victim to sunk cost fallacy - only make decisions based on what you personally expect to have happen moving forward. Although I'll caution you and say that selling low to buy into momentum is a fairly decent way to get burned, which is why I prefer being part of Group 1 than Group 2.