I've used rotaries for years, but they do require an experienced, delicate "touch." Depending on compounds used, it's darned easy to "burn through" paint right down to bare metal with one! It's also easy for a novice to lose control (as with a large floor polisher), and allow the edge of the wheel or the side of the buffer itself to crash into things.
As implied here, they are handy when a reletively large amount of material (paint) needs to be removed, or after a wet sanding. Well-maintained paint doesn't require this apparatus, although an experienced user can apply polish successfully with one using a light touch. Even then, swirls will be present on dark colors, requiring a hand-applied product (like swirl-remover, or butter wax) to eliminate them.
That being said, as time passes, technology replaces the "old guard." Orbital polishers will do the job better, easier, and with more "forgiveness" allowed the user. Technology has improved sandpaper too. A decade ago, wet sanding was done with "ultra-fine" brand paper, that was about 1500 grit. Now, hand sanding can be finished up with 3000 grit, leaving almost a polished finish--much smaller remaining scratches to be buffed away than with the old ultra-fine.
As a side note, always use a cross-hatch pattern on final wet sanding. Those patterns are much easier to remove than long-line patterns. 3Ms orbital sanding system also uses about a 3000-equivalent grit paper, and leaves small circles that buff away with relative ease.
There I go writing a novel again! Just can't help myself--I've "massaged" thousands of paint finishes "back from the dead."