This link also gives a good breakdown. To put it as simply as possible, (and using rough numbers here), but once you get to where you can slot Single-Origin Enhancements, (SOs), you get full benefit from the 1st two of the same type, slightly less value for the 3rd of that same type you slot in the same power, and much less from any after that, (again, of the same type and in the same power). It's gets a little more complicated once you are talking about Invention-Origin enhancements, (IOs), but if you look at the value should you try to slot the 3rd+ of an enhancement, note the % benefit listed, (before placing said enhancement), and compare it to what's listed on the enhancement itself...