Do cats need their nails trimmed?

No..it's not essential or necessary to cut a cats claws. They will scratch & reach up to stretch & circulate blood to their feet..this is not only common for all cats but is part of their daily routine & is important for them. Claws gelp them grip & keep balance..if your cat is not scratching furniture inside the house then leave him be..the scratching post needs to be in clear view but also when he's in the same room, you try scratching the top of the post each time you walk past to get his attention & encourage him over. This worked for our cat..just use your nails briefly on the top of it & it may help him get into the habit. We use to trim the claws of our first cat whilst she was sleeping but to be honest, they don't stay blunt for long & your cat may not like it & feel threatened or uncomfortable..sometimes it's not worth it & your cat sounds fine to me

Scratching on trees, etc does NOT wear down the nails - its sharpens them and the scratching is the cat's way of scent marking the territory.

IMO the cat should have the nails clipped.

When they are scratching outside, they are really just sharpening their claws, and getting the old sheaths off the nail for the new growth... but yes, you can trim them for sure. Just take the tips off, do not cut down to where the "quick" is...that will cause bleeding and his painful and can become infected.