Though my opinion may seem a little extreme, I think that if you qualify for a scholarship, you should apply for it. Sure, you're taking it away from someone else; that's the case with every application. If you have worked hard enough to earn the qualifications necessary for a scholarship, GO FOR IT! It's up to the scholarship committee to decide who will and will not receive the money.
Now when it comes to applying for ROTC scholarships, if you have an appointment, there is no need to hold another full-ride scholarship. By holding it, you're simply making someone else wait longer for theirs, and who likes waiting?
However, if you can utilize the scholarship when it is awarded, then take it!!! You DESERVE it!