RE: Drilling results (via Nitron Detectors)Yes, assays are important as they are "arms length" assessments of what's there by a 1.) qualified and 2.) independent source.
While I'm not sure about gold exploration per se, my biggest copper holding relies heavily on "nitron gun" detectors. This technology allows them to quickly and accurately see what they're drilling through so, as you correctly note, they can plan and/or adjust future drilling and exploration.
The big advantage of nitron handheld units is that results are more or less immediate and, I've been told, "dead accurate." Assays—regardless of who does them—take time.