I don't even know what is emunand. i'm ok in the currently state of hacks. I can play my games perfectly eoven with dlcs so I'm fine to this date
It is short for emulated nand. Which is to say if you have a flash memory chip that holds all the relevant firmware, user data and whatever else you can instead point it at a file on the SD card or somewhere else entirely (most operating systems are fine with this sort of thing as it does not really matter as long as it can read and write fast enough).
People doing hacks like them for many reasons. This includes
You can have two (or more) NAND images which allows multiple people to share a device, or maybe you to just have a bunch of games of a given type on one version and use it as a dedicated device.
You can have a highly hacked version for specialist needs (in normal play you probably don't want all your ROM hacking and cheat making tools), depending upon the security setup you may also want a specially hacked version for certain types of homebrew.
You can keep a clean version of NAND and use another for hacking, if you do it right then if the hacking one gets banned it will not be traced to your proper numbers and your device can carry on just fine. If you get caught normally then the device is banned and all that follows with that.
You can boot an entirely different OS (say android instead of the 3ds firmware).
If you mess up (or give it a young child that will mess something up) the emulated NAND then fixing the console amounts to "eject SD card/USB/whatever it is on, copy working backup onto SD card" and not "bust out soldering iron and manually flash firmware back" or "hope the recovery mode still works".
Some people may not want or care for any of that and live boring (no hacks or fancy homebrew) or dangerously (no care for bans or bricks). To actively oppose or dismiss it though is very odd behaviour from where I sit.