The only time this would be necessary is if the infected file isn't detected by avast, but another scanner. Or if a file is detected by avast, but you don't think it is infected (false positive).
In either case you need to confirm its status undetected or false positive before sending it.
You could also check the offending/suspect file at:
VirusTotal - Multi engine on-line virus scanner Or
Jotti - Multi engine on-line virus scanner if any other scanners here detect them it is less likely to be a false positive.
You can't do this with the file in the chest, you will need to move it out.Also see
(Mini Sticky) False Positives, how to report and what to do to exclude them until the problem is corrected.
