Recall that with the American Express Blue Business Plus Credit Card, you earn 2x Membership Rewards points on EVERY PURCHASE up to $50,000 in spend. After you spend $50,000 in a given year, you only earn 1x Membership Rewards points on purchases.
If you have another card that you would rather use after you hit this $50,000 threshold, then you need to keep track of your annual purchases. It should be easy to see in your online account the amount of purchases you have for a given calendar year. If and when you hit the 50K, reevaluate your future card spending for that year. I am sure going to keep track with both mine and Rob’s spending on our Blue Business cards.