My theory is that the liver can only process so much alcohol at a time (or rather, it has a rate at which it can process alcohol), via the enzymes that it uses to do its job. If you hammer it with three drinks in rapid succession, it uses up its ability to filter alcohol out and has to recharge its stock of ingredients (possibly hindered by all the leftover alcohol in your system, messing up your biochemistry and dehydrating you). If you space it out, it has time to process the alcohol as it comes in, keeping your body from being overwhelmed.

Kind of like how a levy can hold back millions of litres of water hitting it… unless it all shows up at once, in which case it gets overwhelmed and all kinds of problems stem from there.