1 dont wanna bore you with tech and 1m no expert, but in a nut shell, the memo is a tool that you can buy and is useful. in your case of moving tokens from your account to your steem wallet it is not necessary to store all aspects of the transaction on the blockchain ( full trans hash, check sums, content, or whatever) this changes the transaction cost/fee. most transactions such as those are batch truncated and only the bare bolts of the trans are stored on chain, like time/date/amount/wallet addresses... but lets say 1 bought a service from you or your pink boxing gloves for $2k worth of steem. 1 may want a more detailed "receipt" permanently stored on the blockchain (contract parameters or whatever content ). 1 think ill leave it at that and say my bank uses zelle to move money and all you need is an email (any email) address linked to the account... its just as slick as the steem token architecture and allows grandma Lucy to send scrill to aunt Dee whom has never heard of "blockchanged technology" but steem has steemconnect 2.0 (a game changer/money maker) and social media tools too... so its a different animal than Zelle.