This bolded warning is so often stated that one would think it's a fairly common place problem. But after touching many thousands of bikes over a bunch of decades I'm good with saying that cracking at the tapered square axle hole happens, maybe, one time to hundreds of damaged tapers. So for most practical installs, of tapered square arms, I consider lack of tightness to be the problem to be avoided, not overtightening, during the initial install.

Now repeated retightening can wear the arm's taper, as in drawing up the arm on the axle and in time having the axle end's becoming flush with the arm's face that the retaining bolt sits on. If this happens then the arm will no longer be able to be further tightened (without grinding off the axle end a bit). I do see this periodically, just yesterday as example. Having the taper interfaces greased will allow this drawing up to happen more easily.

What I was taught 45 years ago is what I have followed on both customer bikes as well as my own. The arm and axle tapers are dry but for a finger/skin oil wiping. the retaining bolt is tightened to about the 30 ft pounds often quoted (I don't use a torque wrench but have checked with one many times over the years and confirmed the aprox. 30Ft/lbs goal many times). On my own bikes, and after a hundred miles or so, I recheck and usually get a fraction of a rotation of the retaining bolt more tightness (like 2 to 10 degrees of rotation), again using the aprox. same torque as the initial install.l If the bolt saw the upper end of additional rotation I might revisit the torque again a hundred miles later. That's it until the annual going over my bike (which might be around 1000 miles, I have a few bikes that see similar miles per year). On customer bikes I suggest (written on the service ticket if one was generated, verbally if no ticket was done) they bring the bike back after a week or three for a free check and possible re torquing. I suspect very few will take us up on this re checking (the exception often being those who spent $ to replace their damaged arm). On new bike sales the assembly bolt tightening is the same as an initial install and the bike's 90 day free service is when we check the bolt's torque again. This set of procedures have served me and my customers very well with extremely few cases of arm loosening, and those have usually been after a long period on no follow up checks (as in never until the rider feels a loose arm). Of course there are situations when I advice more careful install and follow up checks. Riders with a history of arm issues or those who are extremely heavy do crop up every few years.

As with any mechanical process others will have their opinions and procedures that they have found to work. The above is what I do. Andy