If you think your computer's isn't suffering from any viruses or malware, then that's all there is to it. You might want to delete the virus from quarantine. I mean, if it's quarantined, it's pretty harmless, but hey, the more free space the better, no?
Depends..can avast do an automatic deletion/clean of the virus like Trend Micro and Symantec Anti-Virus Corprate Edition? If it can set it to do the clean first then delete.