I have occasionally contributed some material in the form of a constructive comment, because I didn't feel I had enough information to build into a properly written answer. Moderators have been removing them recently. Sometimes an explanation is posted (as a comment), to explain that I should have written an Answer instead of a comment.
This is diametrically opposed to what I've seen on a dozen other SE sites, where people often contribute via the comment box.
This extreme comment pruning policy doesn't appear to be applied consistently. Various participants have shared information through a comment, attempting to be helpful, moderator Rory included. Example: Baby crying till breathless
It's that much harder to turn a comment into a full-fledged, documented answer if I don't have access to the comment text as a starting point.