The only issue I've read about with mag tubes is in tightening a barrel/mag tube clamp too tightly. Since the barrel is steel and most tubes are Al, you can squeeze the tube, so I've read, to the point that shells won't reliably feed.
I've always been of two minds about clamps. The sound like a good idea, to lock the tube in place, as I could possibly see how if you really bang the tube against somthing, it could get damaged, while if it's on a clamp, it's much more anchored.
The practice of using them though is either they're so tight that they could cause feeding issues, and certainly mar your barrel and tube. Or that they come loose during a range trip, and Lock Tite and such doesn't seem to help.