Rawson is Chubut's provincial capital, a quiet administrative town near the mouth of the Chubut River. It is not a destination to cross Patagonia for, but it fits naturally into a day with Trelew, Gaiman, and the coast.
Playa Union, just beyond Rawson, is the beach piece of the trip. It is windy, local, and Atlantic rather than resort-polished, but it gives you sea air without driving all the way to Puerto Madryn.