Full size breakers vs tandem breakers?

Tandem Breakers on Reliance Transfer Switch? - two breakers in one slot A tandem breaker fits two individual breakers into the size of one That allows you to add new breakers when your breaker box doesn't have any new slots two slot shelving When two breakers are interconnected in various systems the simultaneous closure thereof may be dangerous, or even disastrous Thus, in a multiphase alternating

two slot These breakers are designed to fit into a single slot in the breaker panel, allowing for the connection of multiple circuits in the same space