Box ways (hardened sliding surfaces) give a large contact area that damps vibration and carries heavy cuts, which is why they're favored for heavy roughing and hard-material work — at the cost of more friction and lower rapid speeds. Linear guides (roller/ball rails) have far less friction, enabling fast rapids and crisp positioning, ideal for high-speed and general work, with somewhat less damping under heavy cuts.
Heavy roughing and rigidity → box ways; speed and finish → linear guides. Many machines mix them. See box ways and linear guides, and value machines at The Machine Blue Book.
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