It's only marginally slower, and it's where I have all my stuff. No point in messing with it when it works the same. I never play the DSIWare/Ambassador games I have and they don't work with Gateway anyways.
Plus I'd rather mess up emuNAND and just recreate it from sysNAND than messing up sysNAND and having to get home to my PC and find the right NAND backup and restore it.
EmuNAND doesn't work the exact same, though.
It's slower than SysNAND, and takes up space.
And how would you do anything that could mess up your 3DS without a PC?
Even if you mess up your SysNAND you don't need a PC to back it up/restore. You can leave the SysNAND backup on the SD card to unbrick.