it won't become exhausted by using it once, but it will exhaust faster than if you are using stop bath before the first bath ... the second fixer bath allows the fixer to permiate the paper more and totally fix the image. you might want to talk to bob<?> at rockland colloid to ask specifics regarding their product. while i have used it quite a bit, i don't really know more than my own experience ( experiments ) tell me.
if you can find a copy of "liquid silver emulsion" snatch it up! it has great information about using liquid light &al., making your own emulsons, troubleshooting &c &c ...
unfortunately, it is out of print