Going off of Jeff Rient's recent ditchin' the minis post I've been inspired to post an excerpt regarding my own revelations on dumping minis and moving back to narrational movement. I originally planned on including this in a DM'ing section but I've since decided to adapt it for the combat section so that both players and DMs are on the same page.
"When I originally started writing these abilities many of them had features or effects involving squares and tactical movement. At the time my players and I had gotten used to and started to expect tactical grid based combat. However, I rather enjoyed hexes for their ability to ignore silly diagonal rules and because I had a few lying around so the name was changed to spaces.
Later on when the OSR kicked in to full swing I decided to pick up a copy of Labyrinth Lord. Suddenly I could remember with full clarity the kind of fun, quick and dirty combats we had when I was younger where all you had to do was relay to the DM where you wanted to go and what you wanted to do and he would update his mental map and verbally describe the places and positions or he would quickly scribble up something on a sheet of paper (usually graph paper). I loved it and realized how much I missed it. So I went through the classes and the abilities with a fine tooth comb and edited them to remove all the nitty gritty elements of tactical map-based movement.
In it's place grew up nebulous effects like causing opponents to flee, knockback with the actual direction being entirely up to the DM and the characters attributes. Then I took it a step further and decided that spaces could be a pretty useful, if not nebulous, tool for a DM. You see player character still have a speed, this is represented in spaces which if you desire to use a square/hex map works perfectly well. If like me you'd like to switch back to almost entirely narrational movement a space on the field of combat is whatever you decide it to be.
To some DMs, a space is any increment that places the fencing hero and villain no more than three spaces away from a precarious ledge. To others, it's an increment that causes a melee heavy party to come under projectile fire for a few rounds while they evaluate their lack of ranged weapons (or a big shield!) To that end a space is entirely contextual, in a bar brawl moving through a throng of people is quite difficult and a space may be something as small as half-a-foot. It may be even less if you're crawling through a dungeon scaled down for wererats. While a cavalier jousting will have much larger spaces, typically equal to the stride of a charging mount.
In this way you can simulate terrain and other conditions (moving through a crowd) to slow down characters that would otherwise be represented by some rigid static penalty meticulously laid out in some table in the combat section that you can never seem to find. The table will of course have many obvious situations but you may disagree on the severity of the penalty and there will of course be examples that are missing so you'll have to approximate them on your own anyways. In any event with these parting words let me leave you one important guideline.
"Always be consistent"
Your spaces should be longer for clear outdoor movement than it is for moving through thick foliage, moss covered caverns, and worn down bridges overlooking choppy waves pounding the cliff-side revealing
jagged rocks with every retreating wave. If you created an ad-hoc penalty for pushing through a crowd, remember it the next time it happens or write it down. Consistency is the key to keep verisimilitude while a reliance on abstraction can quickly kill it.