Carpets aren't aborial, they are semi-aborial, so they will sometimes go up onto braches. THe amount of time they climb will sometimes depend on the type of carpet you have. I have experiences with Jungle and Coastal. Jungles will spend a lot of time on braches. Coastals will spend time on braches when young but as they get bigger they tend to just stay on the ground more. I do have branches in my coastals tank but she might move around them but doesn't really rest on them. My Jungle will spend plently of time on logs. My only IJ experience has jsut been with a IJ/Jag cross I got about a month ago that I am taking care of for a friend. He didn't give it any branches becuase he was told they didn't need it. I put some logs in it;s tank and during the day it stays in a hide but every other night it is up on the log the whole time.
So do they need logs. Really no, b ut is it better to give them logs, IMO yes. Giving them the option to climb they will most likely take it. It makes for a better display for you and they can enjoy it, so I would reccomend logs for caprets. You also don't need super tall tanks either like you might need for a pure aboreal snake. 1 1/2 -2 feet high would deffiantly be enough. IF you get creative you can even get some climbing space with a foot tall, but 2 feet would be easier. You can also jsut use a tube if you want to house them if the tube is big enough. And there is no reason why you can't put logs in tubs.