Being able to accurately and effectively employ the rifle in an ambidextrous manner around off-side barricade/cover conditions, using both strong & off-side mounting/holds, makes for a more versatile shooter. Training issue.
It can, however, become an equipment issue if you're required to use a sling which prevents quickly switching the weapon to the off-side shoulder. In fast-paced situations it might prove handy to be able to keep the weapon mounted strong-side and be able to shoot around the off-side barricade/cover available.
Retired LE - firearms instructor & armorer