I haven't been using antivirus programs since 2012 and never had any major issues
of course i don't click in every link i see out there...
At least download malwarebytes or superantispyware and run it every now and then.
Remember that windows 8 and 10 ship with defender aka "Microsoft security essentials" built in. Windows 7 does not. Even if you do browse safely, you wouldnt really know if some rootkit made its way onto your machine. You also don't know if any of your email attachments that you open are 100% safe. You also cannot guarantee that the USB's that you plug into someone elses machine and then plug into yours are safe. At least having some layer of security can alert you.
Ccleaner is a good utility to have although it provides very little security protection.