Pros: Make backups of your physical games and play them digitally (or sail the 7 seas). Homebrew like emulators, ports. Game modding, overclocking, fps unlocking. You can even install Android, and Linux on a modded switch.
Cons: at risk of getting banned, possibly violating your warranty. Bricks are also possible if the mod is done incorrectly, but the chances are very low unless doing a hardmod.
I use a modded v1 switch currently, and I highly recommend it. Just make sure to make emunand as a designated sandbox for homebrew and hacking stuff.