By-products1 are collateral outcomes from an activity which main purpose is not that product. Fairly often, we produce things as part of larger projects without even considering they might have certain value of their own.
When you make something, you always make something else. You can’t just make one thing. Everything has a by-product. — 37 Signals
Work can be structured in order to force by-products and plan what they will be used to. For instance, a book could be a by-product of a series of blog posts, which initial intention was not a book. This approach provides benefits without having to do a lot of extra work, but being conscious from the start of potential by-products can help making them useful without extra effort.
By-products might also motivate you to accomplish large projects. Giving importance to small parts of a big project—understanding those fragments as by-products—contributes towards the completing of the whole thing with tiny steps, getting the project done in modest chunks.
Incidental or secondary products made in the manufacture or synthesis of something else. ↩