Because for a couple of hours work from home, in the comfort of my own sofa, with a beer to hand, I can prevent several hours of pain the following day. It never works for me, leaving my inbox until the day I return and then piling through it. While you’re trying to read those emails, people are giving you all the things they’ve saved up while you were away, new work is arriving, you’re catching up with what happened while you were away and hopefully telling people all about the lovely holiday you just had.
This does raise a question of how far your professional life should intrude into your personal life, but my philosophy is that a productive first day at work will mean less stress that evening, and all week. Lets hope experience bears this out tomorrow!