I think the idea behind either having the generator operating, or even on shore power, when operating the slide mechanism, is just to have some additional incoming charge to the batteries while they are under load... but realistically, since the slide system operates on 12v from the battery, having generator power on while doing it is overkill, or unrequired, especially if you’re ONLY doing it for that purpose, unless your house batteries happen to be fairly low - but even then, your slides will probably still work fine, anyway.
Most factories default to the ‘best case scenario’ in telling you how to operate all things RV related, but it doesn’t mean it’s the ONLY way.
'14 Palazzo 33.3 bunkhouse 34' diesel
KingTailgater2 Dish HD, 100w/5a SOLAR, BlueOx
110,000+mi since '14 - US, Alaska, Canada (also, '14 Gulfstream Amerilite and '07 ForestRiver Rockwood) : )b