Using Time Machine as an external hard drive

I backed up my iMac with an external hard drive using Time Machine; can I delete all the data from my iMac now? My real goal is to use the 1TB external hard drive I just got to store all my music, photos, and other files on. I want to clear all the space off of my iMac, and may by a new Macbook. I want to be able to access all the files from my original computer on either, while cleaning out the iMac. Was it pointless for me to use Time Machine? Thanks so much for the feedback!