Your hands will most likely bounce more like move up and done with you and it can make your hands hard against the mouth
Yes it can make your hand hard at the mouth and it'll be harder to half halt and get a good feel of the mouth.
Not only is it improper equetation but it also makes your hand hard against the mouth
if you do get into the habit of having your elbows straight it will be hard to break that habit later
Nothing will really "happen" it's just not proper equitation.