Being able to move game saves back and forth from a PC would be useful for hacking purposes, and if I could utilize my Everdrive to store save files, I absolutely would. Relying on capacitors and batteries in 20+ year old tech doesn't lend itself to peace of mind, to say nothing of how otherwise inelegant the MB128 and Tennokoe Bank are as extra-backup solutions.
Some of the PCE's ancient RPGs are designed to force you to grind levels or risk dying inside long dungeons with no save points. With a busy job and a baby to look after, my gaming minutes (formerly gaming hours) are too precious to spend like that. Being able to hack in some money or items could make all the difference between whether or not I decide to clear certain games.
An interesting example is Tales of Phantasia on SNES, which is a vastly more enjoyable game if you cheat and give yourself the Scout Orb right at the beginning. This item, which is normally only available if you get through a long optional dungeon at the very end of the game, lets you adjust your random encounter rate.
Finally, once in a blue moon, you can get save-data corruption on real hardware. I actually got it after I had played several hours of Tengai Makyo 2, and I lost the save. Now, I can't bring myself to commit to going all the way through that game in part because I'm paranoid that I'll lose my progress again when I'm much further in. I'll probably get over that and try eventually, but I sure would like an easy and reliable backup.
The same goes for swapping memory in order to play BRAM hogs like Blood Gear.
Wanting to preserve your 100% clear/Level 99 files may be a little silly, but I bet that if krikzz built an easy backup system into his next Everdrive OS, nearly everyone here who has one would make use of it.