It all depends on what you want to be in the future. If you want to be a street sweep, a janitor, a gardner, a refuse collector, then no GCSEs don't matter. If however, you want to become a doctor, a pharmacist, a historian, a geologist, a physcist, a psychologist, a researcher, then they matter a lot.
The better your GCSEs the better your future prospects so far as jobs and careers are concerned.