Some take time off immediately to be able to enjoy their families. My husband misses us. So he uses 1 vacation day right after he gets his vacation weeks. He always plans to take it the Friday following getting it so he can have a 3 day weekend with us.
The rest of it though is scheduled out. We usually know when he will use most of it. Certain days of the year that are important for him to be off. Of course sick days are reserved for actually being sick because we want to know he will be paid should he end up with a stomach bug or other short term illness.
Using all of the time at one time seems irresponsible unless of course they have an immediate need, car broke down, need to make major home repair, sick relative, new child, etc. Just seems the type of person who would take all the time at once just to get away from work isn't responsible enough to plan for "what ifs".