When you should split your notes?

That's a common question that leads to two different approaches and hence generate different workflows: one is having big notes, while the other is having several small / Atomic notes. Here I'm proposing a third approach where both previous ones live together in harmony within the same vault.

The recommendation is really using both approaches of atomic and big notes (Molecular notes?), simultaneously, but not for the same note. What you should do is start with a big note, and once other notes in your vault start linking and needing information from there, you split these parts into other small notes.

There are plugins — including a core plugin (Note composer — Obsidian Help) — to help refactor big notes and embed their contents at the original note. The same plugin can also be used to merge small notes into a single bigger one, so you can test what works better without fear.

Splitting only when needed is a good approach because you don't have to keep, and you don't have to maintain, many small notes that are mentioned only at this “big” note and nowhere else. Having it split would make navigating and absorbing / using that information harder due to the number of hops needed to see the whole picture. On the other hand, when the information is needed elsewhere, you split the original note and start with contents reuse, creating a single source of information for both the new note and the original note.

Using the same terminology as it is usual, these mimic an atom. An atom alone decays (we forget the context and the information) and can't be used for anything. A set of atoms build molecules, and those are the magic part of building our universe of ideas and knowledge. Atomic notes must be grouped to make sense. If you won't group them in other molecules, don't split your molecule of information, keep it stable and useful.

In the end, using Obsidian effectively is all about defining your workflow and finding out what works better for you. Many things are a matter of preference, but if designed purposefully in advance this might save some time in the future.

Just be aware that there are things that are what we usually call “premature optimization”. In my opinion, splitting notes only to say that they are small / atomic, without a real benefit, is a premature optimization and the above rule of reuse helps to prevent that.