In many situations simulating games, I need to (for example) roll extra dice depending on what I've already rolled. (For example, in Monopoly, you roll 2 dice, and if they are a pair, you roll again). This can be approximated by rolling as many dice as you might ever need and simply ignoring the unwanted ones, but the number of results rapidly gets very large that way, and the calculations get slow.
It would be helpful to be able to only generate results as needed. This may already be possible, but I couldn't find a way from looking through the documentation (so if it is possible, could an example be added to the docs? :-))