If I have an alpha reader, it's for a very specific purpose and the knowledge that I have probably lost the chance of having that person as a beta. This is fine with me, as I usually don't have trouble getting beta readers. YMMV. But I rarely do have alpha readers. I think when I started a new age category, I got an alpha to make sure I was in the right ballpark; when I tried something experimental, I got betas early in the revision process to make sure it was worth pursuing the avenue I was taking the novel in; and when I wrote my trilogy, a book 2 beta expressed interest in book 3, which I had just finished. But my first drafts are pretty clean, and I'd fill in any known holes before sending to anyone, even at the alpha level.
The last thing I need when I'm writing a novel is critical feedback of any kind. I'm all ready for it from betas (or alphas), but I need to keep motivated to finish the novel, so an alpha reading as I go would be awful...unless they were someone I used to give me only positive feedback. There are places where I can share and get only positive comments (NaNo threads, for example) during the WIP process, but I don't expect anything I get there is more than encouragement.
The last thing I need when I'm writing a novel is critical feedback of any kind. I'm all ready for it from betas (or alphas), but I need to keep motivated to finish the novel, so an alpha reading as I go would be awful...unless they were someone I used to give me only positive feedback. There are places where I can share and get only positive comments (NaNo threads, for example) during the WIP process, but I don't expect anything I get there is more than encouragement.