flipping over to browse the web the moment you have a couple of minutes free is probably why some companies block access. Employers expect their employees to focus on their job and not flip over at every chance. But what the blocking means for us is something that they ll never understand..
What do you expect engineers to do while code compiles? And flipping to a browser could also mean checking e-mail, filling out expense reports, or scheduling a design meeting. The problem is: even if those things are a productive use of an employee's time, they still interrupt your flow.
I think you got me wrong. I'm one of those engineers who flip over :) What I meant was that the employers do not understand this behavior and all they could do to prevent this is to block access to the Internet which actually harms our work more.
Sometimes, that means more than just paying for the machine on the engineer's desk, it could mean spending money on a cluster of machines just to do distributed compiles. That's also money well spent. Basically, any time you can keep an engineer from interrupting flow by spending money, it's a decision worth careful consideration.
As an extreme example, Google spent millions on SSDs for its source control systems to speed up submits. Money well spent.