It keeps your applications in a small (i.e fast) cache, so it's more or less instant when using it as an app finder. I think it, yes, uses the Spotlight index

It keeps your applications in a small (i.e fast) cache, so it's more or less instant when using it as an app finder. I think it, yes, uses the Spotlight index for finding files, although I wouldn't be surprised if Alfred does some clever stuff on top of it too.