[Bruno]

When I play online, I make use of MapTools' great vision blocking and fog-of-war tools, which require a little bit of preparation for lots of payoff (in my opinion).

When we play on the table, I generally draw it in with dry erase markers as the group progresses - but with exceptions. Sometimes I prepare a large map wiht lots of details, and I preprint it (and tape the pages together) because I don't particularly feel like replicating it by hand. I've covered up parts with paper, but if it's mostly a large open area or outdoor, I often just plonk the map down.
My face-to-face group are all GMs (we rotate the duties) and are good at firewalling information.