One should not look to be unreplaceable, but rather the opposite.

Only when you become replaceable at a certain task (or able to delegate it) you can progress to do new (more interesting) things.

It could go either way. Some places will like and promote one to do different/more interesting things. Other places will eliminate the position with k, thx, bye! Moreover usually people have only so much energy to be always concerned with job / career growth/ changes etc. They are fine their little pieces of knowledge that make them useful at work in a unique way.

If your company has a habit of firing people that share information, or punish employees who work smarter instead of harder, it’s a sign that they might be out of touch with value creation and will eventually be punished by the market.

Being fired from such a place might actually be a blessing, not a curse.

Is this true, though? After seeing enough bone-headed management decisions, I wonder if the bosses even know or care about documentation when making decisions to fire someone.

From my point of view, the lack of documentation might be a reason to fire someone.