I was just thinking about this. I think in many cases I would only want the map for the combats, with something more abstract/evocative in between.
Which is really the same way we tend to use battlemats at our table. All TotM until initiative gets rolled.
There you're mistaken, IMO.
Being able to navigate through the larger map creates actual suspense; the players have no idea where the enemy is, or might pop out; or where traps lie. Formation and teamwork becomes all-important as they move to keep the soft targets covered, and retaining readiness for an attack. We've spent an entire five-hour session in tactical mode, each player moving his pogs in turn, commiserating, speculating, with fights and ambushes springing up, the party recovering, and moving on (or getting hit by creatures investigating the noise).
You can tell an entirely different story with a VTT, and most importantly, the players will experience it together, with the same image, and watch as events are dictated by their actions and decisions.
Using a high-def high quality map means the players literally see the dungeon clutter for themselves, the moss, puddled water, and cracking stone, leaving the GM free to comment on sounds and smells, while giving much more on-the-spot thought to the party's choices and decisions.
It's the difference between stick drawings and art by Larry Elmore.