So adding affixes has a chance to remove... "forge potential" (FP ?) if I'm remembering the term correctly.
I don't recall that Improving an Affix tier consumed any of the FP.
If that's the case, then can every item eventually have a max tier affix after farming a bunch for items to break down?
There are 2 extra tiers of affixes (6 and 7) which you can't just craft on like normal. They are generally drop only tiers but with some of the new runes that we just added, you can manipulate Exalted items to get the T6/7 mods on the affixes you really want.