Buying in for the max is generally better so that you can fully capitalize on your opponents’ mistakes. One of the most common mistakes people make in 5/5 is that they call too much. When you only have $300 in front of you and you make a big hand, you can only make $300 from your opponent rather than 1k. Also, if you have a short stack and find yourself in a big pot on later streets, you’re not going to be able to bluff as effectively since you won’t have many chips to do it with so it takes some of your tools away. With that being said there are some advantages of playing a short stack and plenty of profitable players do it. It just requires a different strategy.