Not so much tbh I don't even bother to watch pre season games. However imo:
- These games are basically training matches. The pressure is off and the defenders tend to be less dirty and combative so if an attacker does well it doesn't really mean much. But if he doesn't do well in that environment it's unlikely he'd do well in the first real matches.
- If a coach plays his first XI in those matches it means he's not very confident of his first XI and would need to let them play more to gel, to get sharpness and to identify issues. If he play the youngsters a lot that means he knows what his first XI could do, they're pretty ready and he's confident of them. He only want to see a bit of what the youngsters could do while saving the first XI for the new season.
So in fact if you see a lot of the youngsters in those matches regardless of the results your team would generally do well in the first games of the new season imo.