Some multi-table tournaments at FullTiltPoker.net offer late buy ins in order to accommodate more players. Buying in late is generally a poor decision, since a good player will be wasting opportunities to increase their chip stacks with the longer playing time. Essentially, buying in late is the same as buying in at the tourney’s beginning, and then never playing a hand. The longer a good player is at the table however, the more chips they will win.
The main argument for buying in late is that you will avoid busting out early on in the tournament. This is faulty logic, however. The potential for the chips that you would win far outweighs the chances of busting out early. A decent player does not let themselves become pot committed to a hand that would not win over the course of the long term. What this means for a good player is that they will gain chips during the late registration time far more often than they would lose chips—given a large enough sampling. Buying in late then, is essentially putting yourself at a disadvantage.
The disadvantage is not a large one, though. If you are lucky, buying in late will not cause you harm. Still, if at all possible it should be avoided since that small disadvantage that you are given can be enough for you to stand the chance of losing money should you repeatedly buy in late to tournaments.