It depends on what you do on your PC.
My gaming PC doesnt have an AV since i want it to be as fast as possible to play games on very high graphics settings which require alot of memory but my old crappy PC who just download stuff and surf the web needs one for sure if i dont want to format this piece of shit everydays.
Also, there is alot of ppl who aren't aware that free pr0n/cracks sites are 100% trojans filled so stop going these sites!