Have you ever made significant changes to the adventure while running it by changing the map, player handouts, or non-player characters?
My background is software development. One of the principles I learned was documents are never finished. The requirements and specifications change frequently. I apply that concept to adventures.
I am not sure if my players realize I routinely change maps on the fly. For example, a while back the party was exploring a dungeon. I accidentally revealed a part of the map of the dungeon they had not yet explored. While running the adventure I changed the map. Removed corridors and room and added new ones. That is the advantage of a tool like Campaign Cartographer. It is easy to rearrange things.
Sometimes the players state they are worried they will run into some specific monster or situation. I always note those ideas. I usually add those ideas to the campaign a few adventures later.
If you want to use your own maps with Roll20 and other virtual tabletop programs you have load them. Usually you have to load them beforehand. The virtual tabletop programs work with bitmap files, not Computer Aided Design (CAD) type files created by Campaign Cartographer (Campaign Cartographer is actually FastCAD with its own set of symbols). For me, I find the ability to manipulate the maps while running very important.
I draw up my maps and label them. They players normally do not get to see the labels. One of the changes I am constantly making is changing the visibility of the labels. When I draw the maps, I focus on how I want the maps to appear to me. For example, if there is a piece of graffiti written on a wall put that on the map. The players cannot see what the graffiti says until they get close enough to read it. I modify the visibility of the graffiti label during the game.
Graffiti can spice up any dungeon. In the 1972 film The Mechanic, Charles Bronson's character leaves a note for his apprentice that reads, "Steve, if you're reading this it means I didn't make it back. It also means you've broken a filament controlling a 13-second delay trigger. End of game. Bang! You're dead." Imagine the party seeing something written in very small script on the wall. The graffiti reads, "If you are reading this it means you stepped on a pressure plate releasing a delayed blast fireball. Bang! You are dead."