Paying for Avast will give you a better overall system protection than using the free version of Avast. Both will give you antivirus protection, but the paid for version of Avast will throw in all the extras such as phishing detection, parental controls, a wider variety of scan options, and protection across multiple devices from one core account. In short, if you pay for Avast, you’ll be protected on multiple fronts, whereas Avast Free focuses just on the basics of virus protection.