DM: "Oooh. The Mummy reaches out and gouges long slashes down your arm; pain radiates through your body and you feel dizzy. Take 27 points of damage and you are dazed!"
Player: "I *snap*."
How many adventures have contained a scene like the above? Players using their precious little rewards cards to avoid being dazed, turn a 19 into a monster-ending critical hit, reroll a natural one (1) on a attack die, make a skill check they failed, etc.? Well, those days are over. As of January 1, 2011, the Player Reward Cards are no longer legal during LFR events. What does this mean for you, the DM?
There are two significant effects right off the bat. First: you don't allow the cards at your table. You can gently inform players that the cards were removed from table utilization per the latest Character Creation Guide. Second: you can expect the adventures to run much closer to the author's original vision.
A third, less obvious, consideration involves DME. Remember, it's our job as DMs to make sure adventures are fun and challenging. I frequently found that doing so at a table with six players holding a full complement of Reward Cards required a significant amount of Hit Point juggling, attack bonus tweaking, and other minute adjustments to keep things interesting.
Now, we can get back to understanding the resource usage the author had in mind for particular encounters, maintaining the pace of the story, and running the adventures. I'm looking forward to it.