Maybe "sophomoric", but it's a start. I've seen very very few successful B&W prints that didn't have the 'bit of pure white and a bit of pure black'. Only the rank beginner (and digital photographer) would stop there.
Originally Posted by Nicholas Lindan
In theory a base exposure of 10 seconds of grade 00 and 10 seconds of grade 5 equals somewhere around grade 2.5. (give or take depending on paper, enlarger bulb type, filteration, etc.,). Like I previously mentioned, the benefit is the ability to adjust the ratio of of the two which effectively elongates the higher values while compressing the low values, or elongates the lower values while compressing the high values. In the digital world, this is known as adjusting the gamma.
Split-grade isn't for everyone or for every negative.