It really depends of your website usage. I am maintaining a free database of chemical properties. Usually people are landing there from Google and looking at a

It really depends of your website usage. I am maintaining a free database of chemical properties. Usually people are landing there from Google and looking at a single page[0] before leaving. To have this single page experience as good as possible, I pack the CSS directly in the HTML. First I packed also the image of the molecule, but it was not good for SEO, because I have quite some visitors coming from search of the drawing of molecules. Google would be smart to index the inlined images, I would switch back to use them. All these optimisation techniques are only good if the context is the right context. That is, you need to pay attention to the assumptions used to make these rules. [0]: https://www.chemeo.com/cid/45-400-7/Octane https://www.chemeo.com/cid/45-400-7/Octane