So the cricket does not hurt the tarantula. So the tarantula doesn't have to wrestle with an over sized meal. So the tarantula can eat the meal later without looking for it or fighting with it. To prevent burrowing or escape of the feeder insect. For little avics i do it and place it in the web for it to eat when its ready. They dont have to look for it or fight with it. Just some random reasons. I can understand why people would not like to prekill a feeder insect though.