Since the points and variable miles option is set to one mile per eligible dollar - if you expect your hotel bill (before taxes et al) to be over $500, then you need to go into the website to change your preference to variable. If you're in a regular Hilton, ES, etc and your rate/total bill is going to be less than $500, you leave it at points and fixed miles? Particularly helpful if staying at one of the less expensive options (Hampton) as that is resticted to 100 miles under the fixed mile option - if you stay two+ nights, the variable miles is obviously the way to go.

Hadn't realized you could change it before each visit - thanks for the heads-up.