Opinions on endmills in ER collets

What are your opinions about holding endmills in er collets. I had a disagreement with my boss who says you absolutely cannot put endmills in ER collets. I agree for heavy roughing to stay away from collet, but when I was a machinist all we had were collet holders and they worked perfectly fine. What are you guys' opinions for holding EMs in ER collets for lighter cuts?