On castle( ashlar) installs like mike has shown, improper installation technique is the norm.
With a near butt install with chiseled edge, sanded grout for most part ends up only in the bevel and not between the tiles themselves, where it's suppose to go.
By definition, an improper install.
You will often see this install with varying grout "fullness"
12 inch polished marble with micro bevel falls in same category
So yes, agitation is preferred over hi pressure in getting grout clean, as well as other process.