For the appearance of industry of course! If I was sat here in my brown chair muttering away to myself, serious questions could be asked about my grip on reality, whereas determined tapping away at a keyboard is generally viewed with benevolence and may even be construed as work. It does depend on what you’re typing naturally, but if it remains unread, no one will be any wiser.
I once worked in a chocolate factory, where the machines were temperamental and the production line was frequently shutting down. As the staff were generally idle types, this was usually a good excuse for lolling about, eating chocolate and casually flirting with ones female colleagues. The supervisors didn’t like this and expected us to do something constructive, like work or something. Cleaning for example. I worked out that all you needed to do was appear to be vigorously scrubbing a conveyor belt with an imaginery cloth to be rewarded with a glowing commendation such as “Why can’t you b*stards be more like him?” Me being the him. I think blogging must be much like that.