Personally, I would never buy a brand new cue that way, if for no other reason than for for eventual resale potential. I have only ever bought butt-only cue that was heavily discounted and needed refinish as a fun project. As you also mentioned, I happened to have several spare shafts on hand, including one with matching joint ring. But it was a pretty beat up cue in need of refinish.
I'm all about keeping as many options open for myself as possible.
Even if you are exclusively using LD shafts and think you have no intention of ever getting rid of it... Things change, and a time might come when you want something else, or simply need to move the cue to get your hands on some cash. Assuming you keep the cue butt in excellent condition, having the original maker shaft available puts you in a position to eventually sell a complete cue with original "unchalked" shaft puts you in a position to get a premium for the cue and appeal to a much wider audience. Plus, you get to hold onto your trusty, favorite shaft.
Complete cues with matching joint rings sell for more, and likely much faster... And in the case of Schon, most people buying those cues want to see that name on the shaft, too.