D&D 5E Exploration: What are the benefits of drawing a map?

[HarbingerX]

Discovering secret rooms is cool n all. But it was always painful to have one player there laboriously drawing out on a grid and asking the GM, "wait how many feet by how many feet?", while every one else just wanted to keep going with the game..

In our megadungeon crawls I draw on a battle mat and the mapper transcribes from there. Eliminates all the needless description of what they should be able to gage visually. I will take a glance at the map they make at the end of the session and only correct mistakes that should be obvious to them.