This style says ‘it's a draft’ ‘it's an idea’. This is very important for communication within the team. It also allows you to concentrate on the essential points and not on the details (I don't like this font, the centring isn't perfect, etc.).
To my great surprise, even for training courses, this style encourages questions and interaction with the students. There's a whiteboard feel to it which suggests that the presentation isn't set in stone.
Right. The more polished a rendering is, the more people are emotionally attached to it. Keeping it rough enables brainstorming, whatifs, etc.
Ages ago, when CAD was new, architects would show customers tracings (of plots). For all the same reasons.
The practice was so common that my buddy (also an architect) created a "hand plot" driver for AutoCAD. "Messy" hand drawn look instead of precise line work. The driver was huge popular.