Typically, OT is paid at a higher rate on many pay scales. So, some see the OT work as a pay raise for doing the same kind/type of work.
Some say that "compounding interest is a working man's best friend." That may be true, but if so, OT is maybe the working man's second best friend.
As a salaried employee, I don't get the benefit of OT, but I'm not complaining.
OT is a benefit to the employer. There are usually fixed costs both monetary and others such as regulatory, legal, training, and etc, for having an employee that are not seen in the hourly rate. These fixed costs may make it cheaper in the short run to work OT than to hire another worker.