>>Lower ISO values are almost always desirable because image noise (graininess) increases as ISO increases.
This was true for film, but the situation is different now. With digital sensors, noise is directly associated with lack of photons. The darker something is, the fewer photons you have, and at some point (often called a noise floor) what information you have in photons is overwhelmed with noise.
This is not obvious because, in any of the 'auto' modes, the camera will use whatever setting is not auto, the ISO you set and scene brightness to calculate the setting it is automating (for instance in auto-speed (aperture priority), the camera looks at the aperture and ISO you set plus scene brightness to calculate speed. Took me a while to twig (ex film guy here). On recent Nikon DSLRs, ISO is pretty much just a gain knob (AKA 'ISOless").
The reason not to use high ISO is that it's so much easier to blow out parts of your shot if it isn't uniformly dark.
That said, I agree 100% on not advising entry level photogs to use features their cameras don't have.
Although I'm probably sounding a bit annoying here, it just wouldn't occur to me to just give some budding photog advice - unless they straight up asked me.
