I overheard a conversation between an IDPA member and someone from the Tiger Team years ago. So take it for what it’s worth.
When asked about comps, they said they didn’t permit them because of the stage description required shots to be made from retention, depending on the comp/porting, it could blow hot gassed/debris into the shooter’s eyes.
How true this comment is/was, is beyond me. It may have just been old guard mentality. But it stuck with me. I love the idea of porting a gun that I would carry but have always been concerned about the hot gasses and/or debris that may be blown up into my face if I had to shoot from retention.