A lot of people in the scrim scene choose to use iron because it invokes a higher level of strategy, Because you can't stand strafe and be extremely accurate all the time, this requires you to be positioned better to have a higher chance of winning your gun fights.

By having the chance to choose between holo or iron it lets the people choose to use what they prefer, this is good because a lot of people play "PAT" or "RTG" only play it because they let you choose between iron and holo not the maps.

Scripters who use iron are very beatable close range and far because it doesn't let you just shoot a laser beam of bullets perfectly every time, this makes it so the people who are scripting will lose to legit players more if they are forced to use iron over holo.