Can we deploy Web Site scoped Feature (Scope="Web") to Site Collection(Scope="Site")? I think applying force command in powershell creates unwanted trouble. what is actual business case scenario of doing that?
AFAIK no. If you deploy a web scoped feature to 'site collection', it will be actually deployed to root web of a site collection. It will still be accessible through Site features link in Site settings, and not through Site collection features link.
Force flag has nothing to do with the scope.