Also, wood is porous and holds onto microorganisms and parasites really easily, so sterilizing it before you add it to your tank is a no-brainer.
If you're adding wood to your tank, you'll probably have to do some prep work - especially if you just picked it up off the ground somewhere (Yeah, we've done that). Untreated wood leaches brown stuff called tannins into your tank that can darken your tank water and lower your pH. They're not harmful to your fish and can actually be beneficial, but unless you're trying to set up a blackwater tank, they might not be attractive to you. They can also sometimes make the tank water so dark you can't see anything. Also, wood is porous and holds onto microorganisms and parasites really easily, so sterilizing it before you add it to your tank is a no-brainer. Boiling sterilizes and gets rid of a lot of tannins at the same time. Not sure you'll ever entirely get rid of the tannins, though.