Guys Im tryin to make things run smoother

Today, i started cleaning my computer of useless stuff::: LIBRARY folder is using a total of 17 gigs...and application supp. is using 8 gigs. What dont i need in there... Garageband is 3 gigs..can on rewire garageband inside Logic...if not its useless to me...also...Are there any useless folder on my comp that I dont need that are huge? thanks

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