At best, it makes no difference to employers. If I were hiring someone to run assays or to do marketing data analysis, it would actually be a negative that they also had a foot in some other profession, because I would be afraid they’d drift off to do that other thing.
Double majoring is often brought up in these forums, as you can see if you do a search (for example, http://talk.collegeconfidential.com/college-majors/1845850-double-major-questions.html). Tellingly, it’s almost exclusively brought up by or for people just starting or about to start college - the idea fades for many as the difficulty of college sinks in.