Can faulty relays cause fluctuating run performance or will they either be on, off or intermittent?

Car is experiencing reduced performance as well as stalling. Assuming these are caused by the same issue is it fair to say it cannot be a relay.

Reason is because, as far as I’m aware, a main relay will either be on, off or intermittent by virtue of being a switch and do not determine amount of voltage delivered etc. therefore it they cannot be causing reduced/fluctuating performance issues such as a fuel pump receiving less power.

Just want to ensue don’t waste my time looking at relays for fluctuating or reduced performance issues.

Thanks.