I know that I can consume both my unit's turns at once by moving past the "blue" movement radius and into the "yellow" sprinting radius. I feel like this is a fairly cautious game, so I tend to move my units one move at a time.
Why would I want to sprint, besides speeding up a unit's turn?
Besides not being able to take further action when I reach my destination, are there other drawbacks?
The big disadvantage of sprinting only happens when you do so into unknown space. Sprinting into an area, only to uncover one or more "nests" of aliens is a quick way to get your face plastered onto the memorial wall.
In most cases, you want to split your move up, just in case your first 'half' of a move changes the tactical scene. There is one benefit to sprinting, though -- reaction fire takes a -20 penalty to Aim against a moving target. It's not a benefit you'll see often, but dashing into safety might be the best option if one of your squaddies is surrounded by hostiles, or being suppressed.
In addition to Raven's answer.
Sprinting also takes you directly to your destination, while moving in tho steps through cover doesn't, which means that most times the distance you can cover by sprinting is greater than by two steps.
