Playtesting is indispensable, but the goals and methodology can vary a lot. For external folks I typically do self-reported playtests (ie, not literally looking over their shoulder) but if we're playing internally it's very easy to screenshare.
You can basically test for anything so usually the goal is to evaluate a specific portion of the game, typically for me it's the tutorials and general system understanding. These are the areas I am not the best at so it takes some iteration. For The Banished Vault we also understood the game wasn't for everyone, so a lot of feedback was negative (our friends and family being honest!) but was generally still pointing us in the right direction.
