Is it the storing of coins part?
Ya that's right, storing of coins wallet is a big advantage to users that are using this particular app.
You have your point there, in long term wise if the users amount grown to a huge number wouldn't the wallet app be more of a hindarance rather than advantage as it will slow down the whole platform.
I does not see this as a problem as long as meritt protocol is able to come out with a good platform with good support and technology this does not pose as a problem to the application.