They don't do anything. Leave them home to sulk on the couch. Avoid whereever possible. Usually, sentences can be re-arrange to make them more active. They clutter your point and steal sunshine.
Weeds can kill a garden and impoverish the soil.
Substituting the thing itself will improve your writing. There will be less pointing and more stating. Always be specific. By doing this , the Empire was hoping to crush any more insurgent activity from the colonies. However, this only motivated the colonists more.