I so disagree, and I'm not accusing anybody of cheating.
This is going a bit OT, and I don't want to hijack the thread, but your comment deserves a response and I would like to explain where I'm coming from.
I've been running a campaign on FG since last October. Both I and my 3 players are completely new to online gaming and 2 of them are completely new to D&D. 2 of my players are partners and have been playing using the same phoneline connected to 2 machines, one an up-to-date gaming PC, the other an old laptop. They've had problems with the length of time it can take to "acquire files" at the start of a session, particularly to the laptop; in one instance, it took over an hour for the player using it to fully download. This has caused problems when, assuming that the fact that players can activate their PCs indicates that downloading is complete, I've attempted to start a session by sharing a map that hasn't completely downloaded, and all the players get is a black space with lots of red question marks.
Things have improved, the laptop has been retired and I've learned from experience not to share too much material at one time, but downloading can still take 15-20 minutes.
As the DM I need to know when my players have finished acquiring files so I can start the game. Unless I've missed something, the only way I have of of knowing this is if they tell me, and the only way they have of knowing it is if they have the console open and can watch progress. Inevitably this means they will see things I don't want them to see, and no cheating involved. It's not a game-breaking issue, but a lot of the magic of D&D is about exploration and discovery and I try to create maps that build on that. A lot of the magic disappears if the players know in advance what sort of terrain or structures they're going to encounter.
As for changing things on the fly, nah. If I've spent days carefully preparing a detailed complex map, with everything stable and in the right place, the last thing I want to do is faff around changing things right at the start of a game, especially if everyone's been hanging about waiting for somebody to finish downloading. There'd be hell to pay if I started doing that.