Should I cite every study that supports my point? Suppose I'm writing a paper and at some point in the paper (e.g. the background section), I write that "Vanilla ice cream is healthier than chocolate ice cream." I search EBSCO and find check all research studies that tested this and find and skim through 15 papers all supporting this claim, including the earliest pioneer research in the area up to the most recent. Is it then appropriate to affix in-text citations for all 15 of those studies to that sentence? What about if I find 50 studies?
It depends on the purpose of the paper. 

If it is a review article on the effects of different flavor of ice cream, it may well be appropriate to cite far more papers than it would be if you are merely establishing the point in a paper containing your original research on the subject. In the latter case you may even be able to cite someone else's review.

Generally speaking, new papers in a field only get published if there is an element of novelty to them. Thus it is unlikely to find 50 different papers saying exactly the same thing. If you need the citation to support your own project, you should be able to find a small subset of those that are most relevant to the question at hand (e.g. if I am using mouse models, I should probably cite prior work in mice over prior work in rabbit models). If you are reviewing a topic, you should be able to find the most important papers out of the group (e.g. the ones that were transformative to our understanding of ice cream health effects). 

Additionally some papers will vary in quality or scope. Citing an initial, limited scope paper might be appropriate if you are discussing the history of a topic, but if you are just trying to establish a basis for a claim you may want to go with a later, more definitive study.

Many publications will give you a citation limit when writing for them. So you often won't have a chance to cite an entire library of previous work. You need to be able to pin down the papers that are best suited for your specific need.