As I was informed 3 months ago, your initial application when "granted" is valid until one leaves the country and then, upon return, a new application is needed and "granted".
I went again today, I arrived at 10am and was number 1. A second IO said I needed one, upon showing him my issued form he said yes he was the IO who granted it. Obviously a hot topic for the Thai Immigration officers.
Just another piece of paper stapled in your passport to keep safe. I presume there is a fine if it goes astray.
I'm going to need a larger briefcase.