Can't even imagine any serious touring machine w/o a centerstand, ...hell, w/o either of them for that matter!
First, it's not easy to put it on the centerstand from the saddle, dismounting after flipping down the sidestand is sooo much easier than balancing the bike while getting off, but then the rock-up is easier, safer way to park, & this is all especially true if fully loaded! As someone has already mentioned, it's waay easier to load [or off-load] it if it's on the centerstand, to say nought of performing some of the maintenance chores, ...even just a wash job. The easiest way on [again, particularly when loaded] is on the centerstand as well, just step up on the near-side peg. Could continue ad-nauseum, but the above are more than enuf justification to leave both attached in my book; ...& I'm 6'3" w/ a 32" inseam, can only guess what it'd be like being vertically challenged w/o having both available.