should such positions be studied?

https://lichess.org/analysis/3r4/5k2/8/8/3P4/3K4/8/4R3_w_--0_1?color=white
https://lichess.org/analysis/8/2bP4/2N1K3/8/8/8/k7/8_b--0_1?color=white
https://lichess.org/analysis/6q1/6P1/8/8/6Q1/8/k2K4/8_b-_-_0_1?color=white
...

is there anyone here who has actually benefited from studying positions of this kind? these are complex positions where everything hinges on a subtle concrete variation, highly sensitive to piece placement — and the probability of encountering them in practical play is virtually zero. and yet, positions like these often appear in various chess textbooks. why? how can studying such positions deepen my understanding of chess? another thing is that memorizing these positions is a major problem, given their indescribable variety.

Well, the first one in particular is very useful to know about. You will encounter such situations fairly often actually--and incidentally quite a number of basic endings are "highly sensitive to piece placement."

“... and actually that is enough until the moment one reaches, say, a FIDE rating of around 1900-2000. Beyond that point, greater endgame skill is a must. ...” - 100 Endgames You Must Know by GM Jesús de la Villa (2008)
https://www.amazon.com/100-Endgames-You-Must-Know/dp/9056916173?asin=9056916173&revisionId=&format=4&depth=1

"benefited from studying positions of this kind?"

• Yes

"complex positions"

• Not really.

"probability of encountering them in practical play is virtually zero"

• No, such happens often when two equal players play.

"how can studying such positions deepen my understanding of chess?"

• Very important to know what positions to aim for and what to avoid, and how to win.

"memorizing these positions"

• No need to memorize, you need to understand.

From Averbakh's Chess Endings Essential Knowledge:
"I conceived the idea of writing a popular booklet devoted to the endgame back in the early 1950s, when I was working on an encyclopaedic reference work intended for players of high standard. Out of the mass of information on the endgame, I thought it was important to select the minimum which any chess enthusiast should know in order to handle competently the concluding phase of the game. It turned out that it was not necessary to know such a great deal."