If I'm working in the city, it's easy for me to say "Well, I plan to drink tonight, so I'll cab to the place where I'm drinking so that I'll have to cab from the place after I'm drinking."
When that place is more than a $50 Uber/Lyft/Cab ride away from the suburbs I'm coming from, the options are limited, leaving me to the effort of having to curtail the amount that I drink such that it's safe to drive home. The science I've heard mention is that you can metabolize something like 2 drinks per hour, which is a handy guideline, but lacks so much. 2 drinks of what? 3% Miller Lite isn't the same as 10% microbrews, which isn't the same as 40+% scotch or bourbon. Does that 2 drink guideline cover hard spirits in assuming the worst, or is it assuming the most common scenario of beer? I have no idea.
For me, I tend to prefer drinking at home, or at Uber/Lyftable distances from my home, so that I can be safe, but yeah, everyone's guidance differs slightly, and as someone downthread mentions, relying on choice of drinking safely as judgement is impaired by the alcohol they're drinking is fraught with peril.