It used to be that when you turned "salaried" ("exempt") at a company then suddenly you were working 60+ hours per week and yet paid the same general amount as you were for 40 hours. Going from salaried to hourly for some means that they'll be paid more of a fair wage--when you're expected to be there on the weekend you're paid not only for the hours but for the overtime or double-time rate.
Calculating hourly ("non-exempt") rate is a pain, to be honest. The person might have worked exactly 40 hours for the week but they still earned overtime given that their individual shifts might have been longer than 8 hours each. In some cases, you have to pay someone a different rate to work some holidays.
Possibly the biggest gain the company would have is if they feel that some of the exempt employees aren't putting in the full 40 each week, not putting in the hours results in less compensation.
Some states like California adjust the rules a little. They allow vacation/sick/personal leave time to be applied to absences.
You should make sure that nobody loses their accrued vacation/sick time in this conversion.