You *could* crosschain, but why *would* you.
Extra wear, extra friction.
Look down at your chainline while riding and see just what those gear combos look like. If the bike is making noises, it's telling you it isn't the best way to go.
Its similar to a manual transmission in a car, have you heard what taking off in 3 gear sounds like? Its the way your car says "don't do that".