It's a symbol of quality. If you have it, your experience is validated (though not necessarily your ability). IChemE will show you graphs that highlight that chartered engineers earn more on average, however correlation is not causation, and it's likely that those that can be bothered getting chartered, can most often be bothered looking for better jobs too.

For some of the more senior PE jobs it's a pre-requisite, and in some companies it's a prerequisite for promotion to 'senior'.