The benefits of multi-core awareness by an app depends on the app.

I'd be hard-pressed to believe that, say, "ls" or "passwd" would
benefit, but a multimedia program most assuredly would benefit, and
any programs that spawn child processes via fork() indirectly benefit
whereas those using system() will not [due to its implementation using
waitpid()].

There's no question that a multi-core system overall "feels" faster
than a single CPU system, and it's easy to test by disabling one core.
I find myself doing things on the multi-core systems that normally
I'd have to do sequentially on a single CPU system. The multi-core
systems have paid for themselves (for me) by my time saved.