DE credits are transferable to many schools (not all), especially state schools within the same state as the high school DE courses. But I have seen them not transfer in certain instances too. The key is to look at the big picture (where do you think you want to go to college?) and do the research as far in advance as possible.
This Florida teen graduated from high school and college (BA) within the same week, thanks to DE.
http://www.cbsnews.com/news/florida-girl-graduates-from-high-school-and-college-in-same-week/
A theater friend of my older son’s graduated from high school one year, and college the next (also thanks to DE).
Yes these are extreme kids, and this wouldn’t be appropriate for every high school student. And again, not all universities take the DE credits . . . when I was looking at Vandy I noticed that. But if my son goes to an in-state public university (and a couple of OOS publics), he’ll have about 26-27 credits to take with him.