Sometimes useful. Like, if the setting is Japan, I expect sandals and tabi socks. North America, I expect moccasins. Much harder to justify in a Tarzan movie tho.
I agree that if the footwear is authentic to the clothing it is entirely acceptable ... and I myself had no problem with the knee-hi moccasins worn in the Tarzan Epic Adventures series as it was included from the start ... but the sandals Weissmuller wore in Tarzan and the Mermaids were not a good choice.