nah, no need. but it is always good to have ToS so you have something to point users to. but when you write it, write it in inclusive manner, not exclusive. most people burn themselvs with it. in other words, by default, you guarantee nothing that is not specifically listed. that way you know excatly what your responsibilities are and what penalties, if any, you are liable for. same goes for users and their responsibilities and penalties. but be careful with agreements and changes made to it later on and getting NEW consent from users. again, if it is free, it is waste of time, but it "might" be handy.
ps: even if it is free, be careful if you are handling user data. if the service onyl provides your own data and does not receive or store any user input, then there not much to worry about...although you might damage user data even if they were not submitted into your system so...think about your needs and ymmv.