I stop when the immediate business need is fulfilled.

I see it a lot like tools in your toolbox. You start buy buying the cheapest of whatever it is you need. If you end up either using a particular tool a lot and a nicer/more expensive version of it will make your life better you then upgrade. If you end up breaking the cheaper one you also invest the money into upgrading. You generally find that you are only upgrading a small fraction of your toolbox this way, and save quite a bit of money vs. buying an entire set of expensive professional grade gear.

I see that for skillsets as well. Why waste time on knowing the nitty gritty deep level of something if I will rarely come back to use it again. If I can cargo-cult my way into getting the thing done and moving on I will. If I end up coming back to the thing on a constant basis I will then invest the time into learning the deeper internals/details/tricks etc.