Ok let's play out a little scenario:
My name is Hercules and I really really want to attend UCSF because my dad, grandpa, and great grandpa all went there and it has been my lifelong dream. Plus, my mother is in SF and I want to stay close to her to take care of her, as she has recently been diagnosed with cancer. Oh and my dad died on 9/11 in an airplane. And I'm their only child. So I have 2 interviews and they're both pre December: 1 at UCSF and 1 at Columbia, which is my last choice. I submitted fees and AADSAS on June 1 and I have a 3.9 GPA and 21 AA. Come December 1st, I don't hear a thing and both schools waitlist me. January 16th, Columbia gives me an offer, which I have 30 days to respond to, and UCSF tells me that I am high on the list and offers are being made as they become available.
Now, you had 8 pre-December interviews at schools all over the country, and come December 1, you get 5 acceptances. All 5 schools give you 45 days, but after the full 45 days, you haven't made up your mind yet so you submit deposits (each $1000) to 3 schools, including UCSF(which you don't really think you liked very much, but you don't want to risk losing that spot and your freedom of choice).
So come mid-February, I have run out of time to wait for UCSF and since I have to get in this cycle and cannot afford more than 1 deposit due to my mother's medical bills, I am forced to commit to Columbia. Now she will be by herself as I move across the country to go to dental school, and who knows how I will have time or money to visit her.
Meanwhile, on May 1, your schools find out that you have commited to all 3 of them, and they all rescind their offers. Now that a spot has opened up at UCSF, they offer me a spot. Of course, having already paid Columbia a grand, being buried under debt, and already having made a housing deposit and made other arangements for Columbia, I am forced to decline. I move away to Columbia, my mom dies suddenly and lonely, I am grief-stricken and drop out of school, and me and you wind up as co-workers at Kinkos for 16 the next years.
Thanks a lot.
(I know it's ridiculous, but you get my point. Don't be selfish. You have had months to weigh each school, just make a decision. And yes, schools find out on May 1 which schools you have deposits at and they WILL rescind offers. I have been warned about this "traffic rule" at 3 of my interviews)