I use Google Maps almost daily and this is also my complaint. It's not a hyper-specific use case. Google Maps are good for navigating from point A to point B when you are sure of both, but they suck at being a map. For instance, lack of always-on street names and weird POI handling makes them problematic to use when you want to explore the area you're in.
We would study the map ahead of time, based on the map figure out our plan of action by either making mental notes or notes in notepad, or notes on a map and eventually execute our plan based on the information we have selected.
We no longer need to do that. We can decide "I want to do something around X" , go to X and when we want to do something specific ask maps "Where can I find Y around X"?
Ability to drop pins removed the need to study map to complete most of the tasks. When one stumbles upon something interesting while reading a book, watching a show, scrolling through eater, one can drop a pin on a map so next time that person is in the area the pin is there!
Studying a map ahead of time and marking it up (on the map itself, as we did with paper maps and dry-erase or permanent markers) is a more efficient interface. There's this forgotten principle in UI that users can mentally filter out noise and focus on relevant parts very good; that's what our sense of sight is optimized for. Having to actively search whenever you need to know something is an inferior experience, both in terms of efficiency and because of missing context.
(Also, dropping permanent pins is AFAIK impossible in the Google Maps proper; it's a feature of "my maps", which is hidden somewhere and has weird interactions with Google Maps.)
You are thinking about it as a synchronous workflow. Study map->create a plan->execute a plan. This workflow was the only workflow because it was impossible to execute a search when needed.
Google maps is optimized for a modern workflow. "I'm here. I need X. How do I get there?" With pins that workflow is asynchronous.
For example, I use pins for restaurants. I find/read something about a place I want to try at some point. I drop pins. Next time when I happened to be in the area I see the pins that I dropped. It may happened to tomorrow or three months from now. My alternative is yelp with its sync workflow - search and analyze results of a search or rely on my memory of what place should be around where.