Strict hex adherence - why?

[Skarg]

Yeah, I have mostly not tried to fit terrain to hex grids since I started playing GURPS, which showed it wasn't really necessary.

It removes the relevance of complaints about hexagonal maps not fitting rectangular places, and actually makes me not like overly rectangular-aligned places (which is mostly a modern thing anyway).

However there are advantages to neatly fitting things into hexes, as it means there are obvious answers to what the effects of terrain are. If a wall drifts irregularly through hexes, then there's a need for a GM ruling (or player agreement ... harder in a competitive game) about what movement in blocked or not, whether there's a penalty to stand in each hex partly filled with an wall, obstacle, water and/or rough terrain, etc. etc. A GM can learn to do that well, but if the terrain all aligns to hexes, then there is no question.