i recently purchased a WD 4TB My Book external hard drive to back up my mac. however after setting it up i realized that what i wanted to do was not use it as so much of as back up, but use it as a place to move data and free up my 2008 imac's internal available space so that it will run faster and operate better. as we all know, using the external hd with time machine means my internal hard drive is duplicated and copied to my external hd. but recently, i turned off time machines automatic updates and started deleting files like music, movies, and pictures from my internal hd and letting them only exist on the external drive. so my question is, if i turn time machines automatic updates back on, will these files be then automatically deleted from my external hd? or will it only update and sync what new data is saved to my internal hd?