Most of us GW users like the cheat menu so that is how we justify keeping and using it. Obviously CFW have solutions NTR, and I am not advocating anyone to go out and buy a Gateway at this point (quite the opposite), but if you have it, there are some uses (.3ds when your internal 3DS SD card is full, cheats (already mentioned)). I personally do not use mine much but I like having the option available anyway. A9LH is just supposed to make it easier for GW users to enjoy it (quicker and reliable booting).
Yes, but setbacks I talk about is, not being able to update to 11.0 if you use it, and a lot others. Also 3DS files are kinda eh if you want online access.