Our target play style for combat encounters would be to use battle boards roughly half the time (when there is enough of interest in play that the tactics are fun to play out), and to skip that with faster "cinematic" combat otherwise.
We have not been 100% successful. The problem is the numbers-driven descriptions in the rules. Needing to be "adjacent" (within 5 feet) for abilities such as Protection style fighting, ranged weapon ranges, spell effects and movement speeds are all much easier to resolve on a grid. Running those rules without a board rapidly devolves into sketches with numbers written on them and/or "mother, may I?" style of play because the DM needs to rule who is next to who, and which monsters are in the spell radius. These rulings also quickly get out of sync with player expectations when there is no map and we want to run combats quickly.
It doesn't help that the numbers involved are pretty much all multiples of the base 5 feet. There is no obvious close/short/medium for effects and ranges. If there were I think it would be much easier for the DM to categorize and hand-wave things.
I was hoping that both board-based and no-board style of play would feel equally viable. But the focus on numbers seems to push toward board playing, at least for my group.
We would still like to pay heed to the differences in movement, range, area-of-effect, etc. of the rules in play, at least in the general sense of creature X is faster than creature Y, or weapon/spell A has better range than weapon/spell B.
Going beyond "just don't sweat the details", how can a group like mine play with the D&D 5e rules as written, without a map, but without leaning on the DM to resolve all our questions of "So, am I next to the Paladin?", or "Is it in range?"
Clarifying: "just don't sweat the details" is a welcome approach to solving the problem, but please give some examples of how this works in practice; i.e. which details can be removed and how?
Best Answer
The key does lie in not sweating the details, but the trick is that which is the least intuitive one: positioning!
Follow three principles and theatre of the mind becomes much easier:
Use descriptive detail
When describing a fight scene, say in general terms where everything is relative to each other. You're not used to giving this detail verbally when your habits are tuned for battle mats, so it will take some practice and effort, but it pays off.
But most importantly, don't sweat being exact—exact details aren't necessary, and even entire things you miss or forget will get caught by the next two principles.
Be generous
When in doubt, rule in favour of the PCs. They're competent adventurers, right? If the Fighter was obviously moving into position last turn, assume that they didn't make any trivial mistakes about their positioning. Don't be miserly with the numbers either—if they're trying to get between the Wizard and the Orc and they've probably got enough movement to pull it off, then don't try to count exact feet to see whether they made it or fell short by 5 feet.
Don't sweat exact distances when the intent of the player is plausible to accomplish.
Track intent above all
What are people trying to do on their turn? Focus on that, rather than the bits and bobs of feet, ranges, and areas. Those are tools you can use as rough measures of whether an intent is plausible this round or will take more than one round. By focusing on what people are intending to accomplish with their allotment of time, it's easier to see what's plausible in the theatre of the mind, and you are actually imagining something more interesting. Is imagining 15 feet of movement an event worth spending imaginative brain power rendering in loving detail? Not really. But a careful repositioning to bolster the front rank, or diving away from a lumbering beast, or a steady advance toward the chieftain with deliberate steps bristling with murderous intent—those are worth time imagining.
So don't sweat the truly small stuff—feet and ranges and positioning in general and some kind of "mental grid". Those are just useful rules of thumb for making reasonable judgements about how people can move around, and trying to re-create the grid in your head is a waste of effort and defeats the purpose.
That's the short, pithy version for how to move from a grid-centric conception of combat to a functional theatre of mind that isn't just "now the grid is in my head and everything is harder, why would anyone do this?" For more nitty-gritty details on implementing a theatre of the mind when you've got a grid-based ruleset, my (and others') answers to these questions should provide: