How so? I'm leaning on it making absolutely no difference other than you have equipment built for a single purpose with limited resale value when the difficulty balances out the power.
Uh, well it's the relative difference that matters. You might think okay I go from a GPU farm to an ASIC farm and so does everyone else and now I am getting the same bitcoin as before, with all my new fancy ASIC hardware.
The thing is, if you didn't upgrade, you wouldn't get the same bitcoin as before. You would get less and less until you start to get virtually nothing as ASIC devices push difficulty higher.
So actually, it makes a massive difference. If you want to get left behind and stop making money, stick with GPU