online vs download

I may be forced to use the online version of TT because I do not want to discard my Windows 10 PC. I only want to do one return (apparently this is a system limit??), and I can store returns etc on my desktop (I don't care if they also keep a copy in  the cloud).
can somebody tell me what (other) functionality or performance i might lose with a move do online? (I can also install one of the modified versions of 11 that can work on an older machine (without the security chip), but I dont see the need to do this for any other reason.)

thanks in advance