I've noticed quite a trend over the past few months. While not meant for long discussions, occasionally the comments for a question/answer can extend into 10-20 comments.
I see this is often a benefit because additional points are brought up, clarification is provided in some instances, and even disagreements are civil and show both sides of a more subjective question/answer.
In most instances I simply bow down to what moderators have decided upon and leave things at that. However, it seems surprising to me that moderators are apparently finding it necessary to remove comments when they aren't in any violation of the terms of service. Even disagreements are kept civil in most instances. And discourse DOES breed ingenuity. There's nothing wrong with disagreements. I've seen this happen several times over the period of a few months and simply kept my mouth shut. However, it's getting increasingly annoying.
It is my opinion that unless a comment directly violates the Stack Exchange terms of service, the comment should be left in tact. There is no benefit to removing them. In fact, quite honestly, there's more harm when users realize that the site is being pruned and maintained silently behind the scenes to promote what a moderator feels is valid, not what the community feels is valid.
I think there is far too much comment pruning occurring. I can't state which moderator may be actively doing this. But I am certain it's a moderator since users do not posses this power.