Lots of confusion in the mountain bike world nowadays, between three wheel sizes, several axle standards, Fat & Plus tires, Boost, etc.
So let’s talk about Boost. It’s really quite simple, Boost moves the chain outward by 3mm without changing the Q-factor (pedal stance) of the crank. It basically uses up the space created when high-end bikes stopped using triple cranks.
Also moving the cassette out 3mm plus another 3mm on the disc brake side means the rear wheel axle grows from 142 to 148mm. This improves the angles for the spokes to create a stronger, stiffer wheel. Great for big 29er wheels but really a good thing for every wheel size.
Bottomline: same pedal stance/Q-factor up front for good pedalling efficiency, wider spoke stance in the rear for stiffer, stronger wheel builds. If you want, you can also do the same trick in the front with a Boost front hub (110mm vs 100mm) but that’s optional.
Why do we add Boost to this frame? Because it adds stiffness to the build, because it works well with the wider rims that we prefer and because it creates more tire clearance between tire and chain. Aside from these advantages, there really aren’t any drawbacks now that all manufacturers have started making their components in Boost versions.