I have not done cash but I can tell you this:
In addition to our tips, HAL will reserve 60.00 pp/pd for a total of 840.00 (2 folks x 60.00 x 7 days).
When that total approaches 800.00 they will hit my card for an additional 60.00 pp/pd based on days remaining in the cruise.
This amount is also in addition to amounts I have already reserved such as the specialty restaraunt and excursions.
Our bar set-up was paid for the day it was reserved.
I would IMAGINE the same will hold true for cash...like get a call to your room if you approach the limit.
I hope this helps a little.