If you tip in cash to the 4 main positions, the CM has to first, not lose it. Secondly, he/she has to take it to their office and have it deposited to his account, and finally, request a check be issued so he/she can send it home (or use precious shore time to obtain a money order).
If you tip by charging to your account, the CM automatically gets a check for all the charged tips every 2 weeks.
However, tips are tips and I've never seen any CM object regardless of the way they are given.
It is easier to tip room service with small bills. That is also the only way to tip the porters at the terminal (if you choose to use them).