yea its heavily dependant on the others who apply. Though i applied everyhwere early just to find out early and im pretty confident im getting into the school i want to go to
lets just say that if you apply late your chances might decrease. pretend you apply late and the school can only accept 50 more people but 300 apply. say 150 of these people meet the criteria however the school can only accept the top 50 instead of all 150 who would get in under normal circumstances.
it really depends on the school. i applied early action to all the colleges i applied. its nice because im done with it early, and i find out early. if you are really borderline getting in, it may help you get in because less people apply early action.
It looks good actually to do the early application to a lot of schools, especially ones that are harder to get into because they already have so many smart kids applying that they have to take other factors in.