Do you have to use the Idler pulley?

I had underdrive pulleys on my car minus the alt. I used a 88.5 inch belt(smog bypass) My car was running a little hot at the lapping days with the bigger water pump pulley. So I put on the stock pulleys. The 88.5inch belt is to tight for it now. But, it fits perfect if i just route if over the idler pulley. What is the idler pulley even for??? Do i really need it? Or can i just route the belt from the alt all the way to the power steering??

Ok, ill try it out. My lap days tomorrow, hopefully it runs cooler now. I think the idler was just to put more surface area of the belt on to the power steering pulley. Thanks, ill drive around and see if it works.