I've read on this website and in other publications that when inletting a large ring Mauser 98 receiver and bottom metal that the bottom metal is inletted first then the receiver, I would like to better understand the reasoning behind this and what would happen if the receiver is inletted first then the bottom metal?

I can be done either way. While attending TSJC we were taught to inlet the action first. Both methods work fine and both require the stocker be paying attention.
Steve

On a one piece guard,, you want to always put the bottom metal in first. They are tapered and have a natural direction to follow. Then your receiver, with guide pins installed, can be perfectly inletted into the top. If you do it the other way around, well, it is harder. Now, with two or 3 piece bottoms, it seems to be better to do the top first.

I can't tell much difference, but usally do the bottom metal first, then using guide pins I settle the action where I can leave a small gap between the action and magazine, to allow for tightening the screws and possible wood shrinkage.