The main purpose, every month all of my visa & master cards hit their limits with my spend on adwords & other online marketing. I have talked to banks several times to raise limits but even the raised limits are not sufficient to fuel my growing business. & that results in an abrupt halt every couple of weeks for my advertising.
I had thought Amex with no pre-set limit would be the ideal solution.
But it so turned out that Google Adwords, Godaddy etc. are not even accepting Amex cards for billing addresses within India!
I recently posted a quora question on the same topic. http://qr.ae/RHCZ6V
Will update this post with relevant replies.