It depends on the AI function. For example: say I want to remove the poster on the bill board. Using generative Remove/Fill I would select the poster with the remove brush.
View attachment 294960
AI then analyzes the area around and generates a fill to match. All told less than a min to do.
View attachment 294961
Using your example of mountains in masking you have some landscape options that it will automatically look for like ground, grass, buildings, sky trees, etc., or you can do a manual selection. Once the mask is created you make adjustments in the developer panel that only affect the masked area. For example here's an original unedited.
View attachment 294962
Using LR's AI masking it finds the following things in the landscape.
View attachment 294963If I click on mountains, it will mask the mountains. Here I raised the exposure slightly and added more blue
View attachment 294964the vegetation is obviously needs work, so here, I clicked on vegetation, to create a mask of only it, so I can work on it only.
View attachment 294965
The newer AI heavy presets, use AI to create multiple masks in a stack and then automatically tone map your image to for a certain look. Invariably you have to go back and tweak each layer manually.
In PS you have the option of generating a text to image layer, or even a whole image. You type in descriptive terms and it produces an image. I use this frequently when I need to do a background swap. Saves a ton of time.