Automatic deletion is only possible into Professional version.
In Home version, the Silent Mode has two options (general answers):
'No' means that all avast! questions that would be displayed on the screen under common circumstances, will be replied 'No' or Cancel, i.e., the infected file will be sent to Chest.
'Yes' means that all avast! questions that would be displayed on the screen under common circumstances, will be replied 'Yes' or Ok, i.e., pressing the OK button will be simulated and the scanning will continue (leaving the virus untouched!).