Fatelvis, actually there is no such thing as a "pre-bedded" stock. Every manufactured item is made to a set of tolerances. Action are, barrels, floorplates, bolts, stocks, chassis, etc are all made to be within a design set of tolerances. As long as everything is made to be within the design set of tolerances then everything goes together and works pretty well. These tolerances are due to different tooling, tool wear, different set-ups, metal finishing, heat treating, etc. and are quite normal. But if you take , just for example, 10 different Remington actions and go over them with a good set of dial calipers you will find different dimensions here and there. .001" here, .004" there, .003" over on the other side, etc. Stocks, aluminum chassis's, stocks with internal aluminum frames in the action area have the same tolerance range. Everything sets on the high points and this is quite normal but when guard screws are tightened and tension is put on some part of the system is may result in a bit of bending or stress. However, most of all the components can just be bolted together and thing will work just fine and the rifles will shoot well.
Glass bedding the action to the stock with a epoxy based bedding compound and without any undue stress involved will just mate that particular action to that particular stock reducing any tolerance difference between the two to essentially zero. This may or may not increase the accuracy potential of the rifle, and it must be done with the actual action that will go into the stock and other actions may have different dimensions. It is not a "required" thing, just one of the options you have.
Aluminum pillars in the stock have only one purpose and that is to maintain a fixed distance between the action and the floorplate. These pillars prevent overtighting of the guard screws from compressing the interior material of a slightly softer stock, and have nothing to do with "bedding".
The above is just my humble opinion based on what I have learned in 50 years of competitive shooting and 35 years in the manufacturing end of the firearms industry. Others may have different viewpoints and your mileage may vary.
