What you give away with linking your Steem account to Byteball account is a data that is already publicly available on Steem blockchain. Only thing you do during this process is that you verify that you have access to that Steem account and that is done via SteemConnect.
Byteball Bytes are given away for free because it doesn't have distribution method like mining, so it needs to give all the coins away to users who will use it, but that applies to pretty much all cryptocurrencies that there is no point for them it they are not used.