Is moving between separate attacks of the same spell unbalanced?

As stated in this question, you can’t move between attacks when casting spells like Eldritch Blast as per RAW.

My question is, if a GM would allow this to happen (cast a beam to a creature, move, and then cast the second beam at the same creature) invoking RAI or just because he fells like it, would that unbalance the game in any way ?