Well, for a developer it's definitely a nice safe place to mess with stuff that would be dangerous to do on NAND. You can also avoid a banner brick by testing on an emuNAND first. At least on a normal Wii, autobooting an emuNAND can give leave you with a quicker access to a lot more channels without having to worry about having to enter the SD menu and have it written to NAND every time. (I'm not sure this is a valid point ... yet ... on vWii, though, without the ability to autoboot.) ... or worry that your NAND is already too full of other stuff for a channel to be written from SD (which could happen if you have a large *legit* collection disk games and their coresponding game saves) and there's also the ability to run it through an exploit every time and not mod your real NAND at all on a normal Wii.
and then there are those who have it just because they think it's cool.
admittedly not QUITE as useful on vWii as Wii ... but still ....