At the smaller stakes, I find my stack increases rather steadily. Therefore, I'm less likely to buy in for max; especially shorthanded. My main exception is when I find one of the people who buy in for the max ( often 2 to 3 times min. ) and basically just put people all-in on most of the hands. Against these people, I always go re-buy for the max.

As stakes and table size go up, money is made by winning fewer/larger pots. Now buying in for the max is very important