Just my 2 cents...
If he doesn't initally tune by A/F ratios, he won't know which way to go with the fuel mods to start.
You ASSUME you'll need more fuel when you pull the secondaries, but what about at different parts of the map? Is it rich or lean? No way to tell without an A/F monitor.
If you've ever tuned a bike, sometimes fuel map changes can result in some unexpected A/F results. Sometimes overshooting the target A/F whatever you are aiming for.
NOW, that said, after you get the A/F ratio roughed out, the very best tuners will go back and tune for best power. And yes, ignore the A/F readings for a while.
BTW, there really is NO optimal A/F ratio. 12.8:1 has traditionally been considered optimal for WOT, but some engines like to run leaner (up to 13:1), some richer (12.5:1). It depends on a lot of factors like cam timing, combustion chamber efficiency, etc. Yeah, and ram air can change things around. Only way to simulate that really is to get a wideband datalogger otherwise you're just guessing. And as mentioned above, 14.7:1 or leaner at cruise and light throttle for fuel economy.
Make sure you block off the exhaust air valve when taking the measurments too.