Vibrations close to your ear drum (ie: ear phones) effect::
It does not take a smart psychopath to see you as an excellent target.
Additionally, it dampens your ability to correct ankle wobbles, pot hole drops and slips on gravel.
Still not so sure? A close vibration so close to your ear drum minimises your innate range of motion to compensate for decreased balance, decreasing the ability for your muscles to perform, decreasing your ability to build muscle and burn fat. This means: two people doing the same workout will get different outcomes if one wears earphones. The person sans-head phones will have greater muscle building and fat burning potential ie; they will look fitter, meaner, leaner. If you are not going to do it for personal safety do it for your vanity.
My friend and I were taught some great skills and had a lot of fun - such a serious topic but we had lots of laughs. Erin is amazing - she is warm and friendly and is really knowledgeable and experienced, I did this years ago and am glad I did it again - my friend and I are going to try and do this yearly to keep it fresh in our minds.