When are there reasons to cite more or fewer sources? As a young scholar I was paranoid about accusations that I hadn't read the literature, so I tended to cite lots of papers. More recently, I've noticed an  elegance in relying on fewer of them.

Trimming the fat in general results in fewer citations, but is the number of citations in an article itself of any interest? Are there contexts when loads of sources, or few sources, are preferred?
Assuming you want to be helpful to the readers (without regard for pleasing the authors of the cited articles), this depends on whether you are writing a guide to the literature, or merely explaining facts and results. 

A guide to the literature should include many sources, while saying something useful on these sources. An explanation of facts and results should include as few sources as necessary for the reader to understand. 

Not all articles need to include complete guides to the literature. It is not very useful to write a half-baked guide with many sources but no precise hints of why these sources should be interesting to the reader.