Ripping or tearing from selvedge to selvedge bugs me! It's because the width of fabric has much more stretch to it than lenghtwise (parallel to selvedge). The ONLY time I appreciate it being ripped at the fabric store is with wide back--and then when a knowledgeable clerk first cuts the fabric at the fold and then gently tears it out toward edges one layer at a time.
Because most fabric is not straight on the bolt, I tend to buy about 1/8 yd more than I need to allow enough once it's straighted--using what you call the "fabric dance" (great name!)
I will often buy enough fabric so that on borders that are going to be more than 3.5" in width, I can tear them on the lenghtwise grain--then you get true straight grain borders. I was told when doing this to allow about an extra 1/8" so that the torn edge is not where the actual seam will be (and thus avoid the possibility of a weaker seam).