Halliday & Matthiessen (2014: 425):
There is in fact an area of overlap between prepositional phrases and non-finite clauses; some instances can be interpreted as either, and some non-finite verb forms can be classified as prepositions, for example regarding, concerning, including. In principle, a non-finite clause implies a potential Subject, whereas a prepositional phrase does not; but the prevalence of so-called ‘hanging participles’ shows that this is not always taken very seriously (e.g. it’s cold not wearing a hat). More significant is the fact that non-finite clauses are clauses; that is, they can be expanded to include other elements of clause structure, whereas prepositional phrases cannot. One can say either he left the city in his wife’s car or he left the city taking his wife’s car; but only the latter can be expanded to he left the city taking his wife’s car quietly out of the driveway.