>>5041215
They're both correct. The tanins they leach into the water are either completely neutral or slightly good for the fish, depending on the habitat the species evolved for and how shy/confident they are. A lot of fish come from blackwater streams/lagoons (particularly South American fish) and enjoy the slight murkiness. However it makes the tank look a little less clean from a human perspective so some people really hate it. It's an aestethic choice really, up to you. Some people go all in on tanins and make an authentic blackwater aquarium like this tank by a well known youtuber.

Boiling the wood does two things - removes a lot of tanins (though some will still leech slowly into your water over the following months until they're gone completely) which makes the tank look clearer, faster and it also helps release trapped air inside the wood, which helps it sink faster. Driftwood, especially large pieces, can take weeks or even months of being fully submerged before they finally sink on their own. You can also get tanins out of water easily by adding some activated carbon, a lot of companies sell this stuff (look up Purigen by Seachem for example) which quickly removes organics from the water to make it crystal clear. There are downsides to that though. Organics in the water are beneficial to your microculture and to your plants, so I don't personally add activated carbon to my tanks for the first few months and even then, I only add it for a week or so to polish the water up.