Wilderness areas: I rarely use maps for outside settings, unless there's some specific feature that will affect play, such as a river, sinkhole, or similar feature. Outside encounters tend to require a little less geographic detail, in my experience, though I always detail distance ("The hill giant is about 300' away, and closing"). If there's a circumstance like excessive mud that would slow movement, I take that into account, but don't generally have to map it out. However, spells like
entangle require breaking it down to squares.
Indoors: I map with a battle mat, and I draw what the party can see based on light, low-light vision, darkvision, exploration, etc. I tend to draw features like furniture and so forth, as I always imagine that it will make for an interesting battle (swinging from chandeliers, knocking over tables, etc.), and it never does. Not ever. Maybe once. Players tend to fight around those things. I'm just as bad, because I forget to have monsters leap up on tables and say something insulting, so it evens out.
I have plenty of rooms that don't necessarily fit a grid, and just work out the details as those rooms come up. I try to describe ceiling height in case anyone thinks about
fly or
boots of striding and springing, etc.
I try to map to the edge of the mat, then turn it over. There's always a risk of some meta-gaming based on where the edge of the mat is, but I have plenty of maps that go "beyond" the edge of the mat. I don't worry too much about that level of meta-gaming, frankly. If they're going to figure they can throw that
fireball in that room and roast everything, they'll do it. Barring a ridiculously low intelligence score on a character, I generally feel spellcasters will have an idea of what's a good area to throw an area effect spell. Wisdom scores, on the other hand, are a very different story.
In general, I don't consider a proper map as so critical to the game that everything will fall apart without it. I try and map where I think it's necessary, and when the players request one, and it generally doesn't take away too much time from actual play.
Warrior Poet