First you buy $2000 worth of certs and then you ask about the rules of use??

All of this stuff is clearly explained on the Hyatt site, but...

For your short cut, yes you can use any amount you want during your stay. For ease of use, charge everything to your room. You will have to go to the desk to check out, no video. You will not be offered "change", that is why the certs are sold in various denominations. Say your stay is $2,100. You give the desk your $2,000 (all you have) in certs and pay the balance with cash, check or credit card. Say your bill is $1,833.45. You can give them $1800, or 18 $100 certs. If you have smaller certs ($10's, 20's) then you can pay even more with certs. But unless you want to pay more that your bill, you must UNDER pay the bill (unless it comes out even) with certs and pay the difference another way. In the above case of $1,833.45, use of 19 $100 certs would leave you over paying by $66.55