How generous should I be with citations? I am wondering if it is a bad thing to cite a paper in a scientific publication for a trivial or irrelevant reason. 

The specific instance I have in mind is the usage of certain terminology. I basically want to make a point along the lines:

"We define a set to be flabby if it obeys conditions X, following the convention in [Smith]. We note that other authors (e.g. [Jones]) also require flabby sets to satisfy a condition Y".

Now, it is clear that if you use some definition (which is not very classical), it should be attributed, or at least a reference should be given to some reasonably good introduction to the topic. In this case, the reference the paper of Smith does the job just fine. But what about Jones? The only reason for citing him is that he happens to be using a different convention than I. On the other hand, I cannot convincingly make the point I want to make without some reference; and I'm concerned that I might be confusing the reader if I don't make this point. It could be that Jones gets an extra epsilon of recognision because of one more citation to his paper, which I personally don't mind at all. But it is maybe slightly weird that I cite a paper which I am not, strictly speaking, using.

I suppose this particular case is not really that important. What I am would really like to know - although that's perhaps too vague for SE - is whether it is generally OK to cite papers just because it is convenient for me, without worrying about whether I actually use the results of that paper in my work.

(If relevant, my field is pure mathematics.)
Even things that you aren't directly using may be quite relevant for establishing context.

The only thing that ever keeps me from being generous with citations is page limits.  Otherwise, any citation that fits well with the flow of the scientific narrative and helps place your work in the context of related work is good for everybody involved, and I see not reason not to err on the side of inclusion.