(I'm sure of the first one, less so on the second.)
habits and breaking-bad-writing-habits should be merged. The latter is a subset of the former. Neither has many questions (17 and 10) and they just aren't distinct enough to warrant the need for both.
psychology-of-writing seems different (out of 48 questions, only 3 are tagged with either habit tag). I'm okay with leaving it as is.
All three tags are distinct and should remain
I'll start by quoting the tag info for each tag.
habits: "Writing habits, routines, and systems for writing."
breaking-bad-writing-habits: "This tag should be used for questions that are searching for common techniques to combat bad writing habits that might hinder your progress."
psychology-of-writing: "This tag should be used for questions that deal with the psychological aspects of the task of writing something, such as when asking about the feelings you have before, during and after your writing or about the psychological background of getting yourself to work by for example setting goals and treating yourself to for example cookies after you have finished your current writing goal."
To me, each of these serves a unique role, though there is certainly overlap I believe they are distinct enough from each other to remain.
habits is about the things that we do, though I am only so-so about its existance and would never use it myself I don't think it is a bad tag and it does aptly describe most of the questions where is it used.
breaking-bad-writing-habits is about the techniques to fix our bad habits, not about the habits themselves. Though very related I don't believe they are the same topic. In fact I feel this tag has as much or more to do with discipline as it does with habits.
psychology-of-writing is a different tag entirely. Where the other two tags are about what we do this tag focuses on the why and the how of the writing craft. I feel it does have some crossover with the writer tag but not with the habit tags above.