I've run V20 and M20 on roll20 for awhile now. Mostly I just use an image for the area to set the scene. I'll also use some maps for countries and cities with character tokens as the map pins. Real supported map pins are coming soon and are in beta testing now, so jerry rigging map pins with character tokens won't be necessary for long. If there's a ton of NPCs present (like a court scene), and especially if they're in different of groups, I'll bust out character tokens onto the scene to help the players keep track of who's there and how they're grouped. You can optionally set name plates under the tokens or add tool tips. Only if things are going to be a complex fight do I use an actual combat map. Like a fight in a dead end cave isn't too complex and theatre of the mind is fine. I've had fights that spanned multiple rooms, floors and the roof of a building with the PCs all over the place, so combat maps can be helpful, but not necessary. It really depends on the type of game and your and the players preferences. If you have players that have spatial issues, battle maps can be of great benefit.
