Whilst you can reinvest on as little as $10 it is unwise to do so, interest is paid as a percentage of lend so when the percentage is small say 0.01% on $10 you would get nothing on $100 you would get $0.10 on your lend. On the other hand should you invest $1010 or more you would at least always get 0.1 over and above the current percentage.
What can I say, life's a bitch and favours the wealthy!
Reading again your question I can see no difference other than it is almost a one click service using reinvest.