The circuit that the capacitor is in will only charge it to a certain voltage. So you can usually use a higher voltage and have extra capacity. Even though it's not being used.
Unless the circuit needs low esr. Then adding a higher voltage may mean higher esr too.
Lower tolerance resistors are cheaper. Pull up resistors for example don't need to be an exact value. Close enough will do.
An expensive analogue amplifier will have high persision resistors. On filters and transistor resistors.
