Visual Studio – why are line numbers off by default?

The only time I'm interested in line numbers is when I've given a specific one (e.g. in a stack trace). At that point I want to go to that particular line (which I can do directly) but I don't need to see the surrounding line numbers.

I value the contents of my screen, and line numbers would just be wasting it for me.

I think the bigger question is to ask yourself why you would want to see line numbers. Why are they important to you? In what situations do you need to see all the line numbers for the current page, rather than just the current line (which is displayed in the status bar)?

EDIT: I agree with Michael's answer that for the specific example of pair programming, they're useful. Personally I don't happen to pair very often (I'm happy to do so, it's just rare) and so line numbers are not useful - and are even distracting - for the rest of the time.

Line numbers are essential when pair programming. When two people are working together, it is very helpful to say something to the effect of "There is an issue on line 35"