Several months after I got my Plat. I used the button. I needed to make a purchase for a bit over 20k and it was nice to know they would (and did) approve it. Previously the max I charged was 4k at any one time and was averaging about 7k/mo but I hadn't had the card very long so it seemed prudent to check first.
@LionLaw wrote:
The "check spending ability" button is always mysterious and fascinating. Given how often amex SPs its members, I'm sure your current util % is a factor; while you might get approved for a 10K purchase if you have plenty of available credit, you might not if you've maxed out $25K in revolvers.
I tested my limits a little the first few months after I got my Zync. I was approved for $8K, and I never went any higher than that. My biggest balance ever was about $3500, and I don't imagine I'll have a balance that high very often. I always pay the same day my statement cuts, if that makes a difference. Now that I've got 7 months of cardmembership under my belt, I might test the waters a little bit, just out of curiosity.
I'm at 5 months of cardmembership and have been using this as my daily. While the ring caused me to test $5k, curiosity caused me to test $10k (approved). Now I really am just curious where my internal limit is, but I'm too afraid of poking the bear to try again right now. 
