There are a handful of colleges … mostly hyper-selective ones … that prohibit Early Action candidates from applying Early Decision elsewhere (and a few of these prohibit candidates from applying Early ANYTHING elsewhere). High schools, however, never impose such restrictions. These come from the colleges themselves.
As a college counselor and also as a parent, I don’t have any problem with a policy that allows students to mix Early Action applications with an Early Decision bid, as long as the student understands that–if admitted to the ED school–he or she MUST attend (barring financial aid inadequacies, of course).
This is a particularly helpful approach when a student is aiming for a “Reach” college in the ED round. I think it’s a big stress-reducer when students who are denied or deferred ED get good news from an EA (or Rolling Admissions) institution at about the same time. And allowing the ED kids to pursue EA options also means that they already will have completed some other applications when the ED verdict rolls in. It’s bad enough to get turned away from a first-choice college in December, but it sucks exponentially more to get shut out via ED and then to have to spend the holiday break writing a dozen essays!
There is so much to hate about the admission process that I could go on and on for hours (well, more like days … or weeks!), but concurrent ED/EA is not on my Most Heinous list. Although one could argue that an EA applicant who is accepted ED elsewhere has taken a spot at the EA college from a student who really wants it, you could make that same argument about any student who applies to any college that is not a top choice. So, if I ruled the world (or at least the admissions world), I would limit the number of colleges that each student could apply to (eight is the figure I have in mind). This would spur students to make more thoughtful college rosters and would bring down acceptance rates because there would be fewer students saying “No thanks” to admission offers. But, in the meantime, if students want to apply to multiple EA colleges and then throw an ED school into the mix as well, I have no complaints. There are too many OTHER issues to whine about!