The speed setting is there to vary how quickly your ads will appear on the selected pages.
Think of this like a throttle lever for your ads.
If you want them to display as fast as possible, then select "FAST"
DEFAULT is the default speed for ads, as it works for most members.
If the ads are displaying to quickly for your liking, then select a slower speed.
QUICK NOTE: The speed by which your ad is displayed depends on several factors.
* How many ads are currently running over the entire platform.
* Speed Setting
* How much traffic is visiting the site you have selected your ads to show up on.