Any game that has been a major copy or some sort is off limits. My copy of Blue, Yellow, Ruby, Platinum, SoulSilver, Black, White*, Black 2, X*, Y, and Alpha Sapphire are unresetable for various reasons. Games like Blue, Y, and Alpha Sapphire won't be reset any time soon since they have major stuff on their game cards. Ruby won't be reset since I still want to beat it one day (just Victory Road and the Elite Four). Yellow won't be since I love that save file (though I will admit it isn't completely off the table). Platinum, SoulSilver, Black, and Black 2 are a combination of important stuff (both nostalgic and competitive reasons) and love for those save files, especially Platinum as it was my first playthrough. Also, Platinum and SoulSilver both have access to forme changes introduced in Gen IV that they otherwise couldn't get if I started their files now (the Rotom formes in Platinum and the Griseous Orb in SoulSilver**)
On the other hand, my copies of Red, LeafGreen, Diamond, and White* can be freely reset as much as I want. Well, I need to get a few things off of Diamond, but that's another story.
*One copy of White is will not be reset until I get around to catching its Victini. The other copy (I have two) can be freely reset since it doesn't have an event. A similar story to my copy of X since I am STILL resetting for a decent Diancie.
**Yeah, I still can get that in other copies of the Johto remake since I still have my two Gen IV Arceus.