Privacy - All transactions on venmo are easily accessed by venmo and other third parties.

International transactions - Venmo is very limited in this regard.

The unbanked - As stated already, there are about two billion unbanked people worldwide.

Avoiding banking cartels. - We've fed these parasites enough, don't you think?

Ease of use - A payment over a social network would be relatively seamless, particularly if you believe that apps allowing for rapid transfer between cryptocurrencies will be feasible (they are to some degree already).