Dan Drezner, who just won the title (congratulations!), gives a list. Oddly he leaves off the most important (only?) benefit, namely that no one can tell you any more that you won’t make full professor. I know that sounds silly but in essence you choke off the ability of your university to send you one very particular negative status signal. Nor can they hold that threat over your head.
Sometimes I think this is also a benefit of being married. Let’s say you and your significant other are not married. In that case proposing, and having that proposal turned down, often causes couples to split up. By marrying you remove this scenario as the source of a possible split.
There are advantages to sitting at the very top and very bottom of status distributions; it is often the in-between spots that are problematic.