These are gross oversimplifications but...
In anything but MPH it doesn't matter
In MPH, community hospitals like it a lot.
"Primary Care" fields (gen surg, peds, family, IM) may consider it.
In general, your Boards, Grades/AOA, Research, Letters of Rec, Sub-I auditions, and Personal Statement matter more.
An MPH can compensate for a lack of research because you "did something else" and they "have something to talk to you about." But, if your goal is to do interventional cardiology, its tough to say "i really care about public health! but what i really want is alot of cards inpatient procedural work."
100% Anectodal from people I know say that retrospectively the people not doing a primary care track regret doing their MPH (Uro, Ortho, Optho) because it never came up. People doing Med-Peds and Tropical Medicine (i.e. med programs that let them travel) really thought it was awesome and it helped them in their interviews.
Doing a masters before you show up to med school was just to get in. Everyone knows that.
4 years 5 letters NOT WORTH IT (MD/MPH)