my car needs a lower timing belt cover but the mechanic at the shop said i do not not need one. i think i lost the one i had on my car. is it true that i do not need a lower(thers a lower and upper) timing belt cover? if so, then why did toyota put one on the car in the first place lol.

I think the belt cover is just extra weight. So are the hub caps, valve cover, fenders, hood, doors... you don't need any of them. Why do you need a door to keep you inside? your seatbelt will do that for you and it weighs much less. I think the mechanic at the shop is right... oh, leave him your wallet full of money, that's just extra weight too.
Oh, in case you do intend to drive without doors, please wear pants.