Yesterday I was asked by someone at church if I did any writing over Christmas and my answer was, "actually, no."
Did I feel guilty about this response?
Why? Because I've been busy beta-ing for someone else. I know many people out there can write and beta at the same time. I can too except that I tend to be a slow beta-er. If I feel any guilt at all its because of that and not because I haven't been writing.
I strongly advise not only to get your own stuff read by others (preferably strangers) but to read for others yourself. Beta-ing is like teaching. The teacher gets as much, sometimes more, than the student. I notice things when I beta and then say to myself, I've got to watch out for that in my own MS. These are things I probably wouldn't notice in my own MS in the first place.
My point here (since I can't seem to find the right words this Monday morning) is that beta-ing helps teach you the craft of writing. It's helpful to a writer in all the right ways. So take the time and do it.