Hosts do have a discretionary comp account but are not allowed to use it in all markets. In Kansas City, for example, hosts can use discretionary comps and not touch your points for certain things, in other markets you have to go through your RC balance before a host can intervene. Harrah's does have a sort of RFB which involves them tagging your room incidentals to your Reward Credit balance and if you have 0 RC's they just drive your account into the negative and then put you on a "Comp Restriction" until you dig out. While on this restriction, a host can still evaluate your play and issue discretionary comps.
RFB is really not free. When you are RFB at Mirage, Wynn, Caesars, etc you are still using up a comp balance, it is just a hidden comp balance that you are not allowed to know the total of. The Caesars Connection Card "Comp Dollar" balance, for example, accrues at an anemic rate compared to how fast Reward Credits accrue. It took me almost $1,000,000 in VP action to accumulate about $450 comp dollars at Caesars over a few trips...the same action at Harrah's or Rio would have accrued about $4,000 in comps playing VP and I'd get free rooms which are really free. Granted Caesars also has a hidden comp balance which accumulates much faster than the "comp dollars" but if you're RFB all rooms, meals, shopping sprees, cash offers, etc are deducted from that comp balance. With Harrah's, everything that comes in the mail is really free and I have full knowledge and control over my comp balance. I vote for the Harrah's system.
My biggest complaint about Harrah's would be that at some properties they don't give enough bonus reward credits for your action...(New Orleans is an example) fortunately they make up for it with really excellent mail offers.