People who say why pay for modchips need to pull their heads out of their a*** for starters as they don't seem to know much if anything based on that statement, now that I've got that out off the way....
1. Making a NAND backup should help save you if you brick your Wii from a bad softmod and if you accidently install an out of region update which your modchip failed to block.
2. Modchips actually help some Homebrew apps launch games that would otherwise fail to boot and they also allow the booting of GC backups along with Wii backups. Basically they compliment each other.
3. If your getting a soldered WiiKey make sure you know how to install it or get a professional to do it for you as a bad soldering job can cause damage to the circuitry.
If I can think of anything else to add I'll either modify this post or make a new one.