There is no clean separation between personal and work. It is also more efficient to blend them (if I expect a baseline level of non-snoopiness on my work computer, I will text my boyfriend from my work laptop... obviously beneficial for the firm).

Either way when it comes to ranting about the company: many workplaces don't have a watercooler where all your team mates congregate (e.g. remote/different offices). Also what, you'll rant about confidential work projects over non-work texts?