Every day use as a hard drive
I'm not sure how to interpret your question. By "TC" do you mean "Time Capsule"? Do you have a Time Capsule? How is the 750 GB drive connected to the rest of your system? Are you asking if you can use for other things a volume that Time Machine is using for its backups? If so, that's not a good idea. For one thing, Time Machine by design will eventually consume all the space on that volume, which will cause problems for anything else you have on it. For another thing, Time Machine won't be backing up those files on the Time Machine disk, which means you'll only have one copy of them.