Answers and comments submitted by moderators are given more weight in users eyes, and well they should. A mod's answer is many times the final say on an issue especially if that mod is also an SE employee.
Many times I have seen an answer or a comment and not really understood the dynamic of the conversation it was part of, until I realized that the user had formerly been a mod and therefore his opinion held more weight.
(I know that SE likes to tout that there is little distinction between higher rep users and mods, and for the most part, that is true. But there are things that moderators can do, and knowledge that they are privy to, that makes their opinions and posts more valuable.)
I think there should be some kind of indicator on a post that was written when the user was still a mod, so that others can see that and therefore better understand the conversation. I'm not sure as to what this indicator could or should be, but perhaps a grayed-out diamond, or a shaded username (like a post-owner's comment) would work.
(This kind of calls into question those posts made by a user who afterward became a moderator. Currently, one could assume that they were from during his mod period. Perhaps then the indicator should be one on the answer/comment itself, rather than on his username/flair. This would solve both problems.)
Edit: Thanks to @yydl for pointing this out. This idea that a mod's posts holds more weight, mostly applies to meta sites. However, it can also apply to a main site, mostly to a mod's comments. Perhaps "lo shanu" should apply here.