We are prompted from time to update to the latest version of word press.

When searching for a plugin, it is advisable to click on details, many times I observe a notice that tells you whether the plugin has been tested for version of word press.

Is this the expected process to installing a new plugin?

What happens when an installed plugin becomes incompatible, Is there a notice posted anywhere?

My perception was that all plugins listed are compatible with word press updates, this was arrived at after being told I could not revert to the plugin Sociable, after it became incompatible with an updated version of word press.

Final question, are wordpress updates optional, and are there consequences if you do not update?

Thanks for your help.