Reasons to avoid using (broadband) impulse response to align mains to subs. 

It makes sense then that IR is not a good measurement tool for adjusting timing difference between subwoofer and mains for what we're ultimately trying to do, which is to align the phase slopes of mains and sub throughout the crossover region for good summation. Thus, acoustic slopes, assuming they match a good and proper crossover slope, should sum to a nice flat response in the region. I've found that phase "slopes" of each in the region will show if the sub is lagging behind the mains or mains behind the sub by the steepness of the phase wraps. As you delay a driver, the phase response will exhibit more wraps. So it's a matter of using either delay or phase adjustments in the DSP to make sub wraps overlap the mains throughout, and it's done.

Merlijn, how might someone be sure the have the right delay value if perhaps the Subwoofer naturally/unnaturally lags in its performance? If I just use a tape measure or laser to calulate the proper delay offset for Smaart to read the trace how can I be sure that I've accounted for all possible delay inducing issues, without blindly trusting the physical distance? (Are there even such anomalies in a signal path or are you saying that using the phyical distance is a fullproof method?) ... I'm just a beginner so be gracious with me :)

I have never seen in my career, in the real world, among the guys who work in the world of concert installations and not those who live among books, someone who aligns Main and sub with the delay finder. perhaps the author has seen them in the world of Car Tuning? if this were to happen, it would mean that decades of smaart and mwyer schools have been of little use, do you think? As Jacop said in his comment, the author confuses Delay Fidner with the possibilities offered by IR if visualized and studied with the right tools. And yes, because here it is simply a matter of software not suitable for doing tuning work with IR, which is possible in other software

Very much influenced by your teaching. Thanks a lot. Which is this rta software you are using ?

This appears to be a faulty delay finder issue, not a "using impulse issue". The impulse clearly showed a 10ms start time from original t=0. The delay finder got this wrong but the user could clearly see (as you did and pointed out) this is wrong. The impulse could clearly be used to align the mains to subs, just don't use the delay finder to do so. Might want to update your title to not be misleading. I'd suggest Reasons to avoid using automatic delay finders to align mains to subs.