If you had to pay to rent a truck and also pay to hire workers to move it in and out of the truck and then up 10 floors to your apartment, then yes, it wasn't free, there is a real cost to you. A cost that you saved me because I didn't have to pay someone to take it to the landfill. So I would actually be saving money despite that it looks like I gave it to you "for free". And if I was really crafty I'd have suggested for you to use a particular moving company and then I'd have charged them a referral fee.

(Of course this is a somewhat cynical view, and this isn't even getting into the other costs associated with second hand furniture -- anything with upholstery carries a risk of containing mold or vermin and you may need to pay more to get it cleaned/sanitized)