Using sleep command in ssh authorized_key to prevent user's actions

I'm setting up an Ubuntu server to receive ssh connections from clients so I will then be able to connect back to their machine (reverse SSH tunneling). I searched for a way to prohibit any action from the client on the server, and I found different solutions, but none seems as simple as just configuring the authorized_key of a specific client on the server by adding: command="sleep x seconds" Am I missing something important that would make that solution not a good one?