The only advantage a 30mm tube gives you is more clicks of
moa on your turret adustments.
If you plan on extremly long range varmit or target shooting you may want to consider you may want to consider it but for big game hunting its really not going to give you an advantage.
Its more than likely made from the same thickness of tubing, its just a wider piece of tubing so it ain't going to be any stronger.
As far as light gathering capabilities advantages, generally the answer is it won't be noticeable to the human eye in the field.
It would have to be done in a very controled environment using very soficticted equipment to see any difference if any.
And do that everything, would have to be the same except for tube size and it would be hard to compare apples to apples betwwen different companies makes and models.
To many other factors come into play such as size of objective lens,quality of lenses, type Lens coatings, single or multiple lens coatings and number of lenses being coated and are the lenses coated on both sides or just one side.