Generally, citations are good to have. There are 3 different types of sources:
Reputable sources, such as major news agencies and scientific institutes (The Times, National Medical Institute, etc.)
Personal experience. This is information you have gained from your own studies. This is not info you have gained from reading other sources, this is info you discovered by yourself.
Secondhand personal experience, such as blogs.
Wikipedia is a bit of a special case here, see Wikipedia's own article for citing Wikipedia. (tl;dr: it's mostly good but double check everything)
Generally, the first type of source is always welcome. In particular, questions tagged scientific-studies require answers to be sourced as such.
The second type of source is also welcome. Generally, you should try to present your info in an unbiased and methodical way. Imagine you're writing a research paper using the info you found out (doesn't need to be anywhere near that fancy though, but it should be scientific in the same way).
The third type of source, honestly, isn't always a great source. Unless the article provides undisputable proof (i.e. multiple images showcasing what they mean), you can't really trust it. Anybody can set up a blog that says anything, and that doesn't make it true.
But back to your real question: How often do you need these sources?
Most questions don't need many sources, if any. Obviously, scientific-studies questions need the first type of source, but that's really the only question that requires it.
To quote Oxford Dictionary on citations:
There are only a few instances in which you probably do not need to cite your sources. You do not need to cite your sources if you are writing your own words, ideas, or original research. You also do not need to cite information that is considered common knowledge, such as:
- facts that are found in many sources (example: Marie Antoinette was guillotined in 1793.)
- things that are easily observed (example: Many people talk on cell phones while driving.)
- common sayings (example: Every man has his price.)
So basically, if it's either obvious or so simple that it's common knowledge, you don't need to cite it.
In your example case, I agree that you don't need a citation. I'd suggest linking to the wikipedia article about the 70s/80s and protein combining, but that's it. I wasn't around for that era, so some more info would be nice. However, you don't really need a source, just a bit more info.
However, when in doubt: cite! You can't have too many citations. If it's easy to get a source for anything, go ahead and do it! Better to source it immediately than have to retroactively explain to people who are skeptical.
TL;DR: Use a source when it's not common knowledge. If it's obvious to those who know about it, you probably don't need to cite, just explain a bit more.
In your example case, it's okay as-is, though more info would be nice. (not necessarily a source)
