Nowadays it's not as big a deal because maps are often used just to check the order of stations on a line or whatever, but if you're actually planning a journey

Nowadays it's not as big a deal because maps are often used just to check the order of stations on a line or whatever, but if you're actually planning a journey without using an app, it's useful to know that Finchley Road and Hampstead stations are about 15 mins walk apart despite having a huge gap between them on the tube map. Otherwise you end up going all the way in and out of town and missing the lovely views, or waiting 10 mins for an overground train when you could have basically been there by now.