Pistols were typically not issued to enlisted men in the U.S. Army in WWII save for machine gunners, MPs, and senior NCOs. With that being said, many enterprising Joes picked up handguns they found along the way, typically from former enemy stockpiles to augment their M1 Garand, Carbine or Thompson.
While of course, the guns were valuable as souvenirs, second only to a Gunto sword or HJ dagger, they were also carried and undoubtedly used to one extent or another.
Likewise, the British, Canadians and Australians were also captivated with second-hand Axis pistols and were frequently seen carrying them.
Poetically, William Joyce, AKA Lord Haw-Haw, was shot in the butt by a British soldier with a captured P-38 while being taken into custody near the Danish border in May 1945.