We have done it several times in different scenarios, one customer owening adjacent buildings, two sides of twins 2 owners, or 2 separate adjacent neighbors flats at same time.
With flat roofs, depending on size, can save you a lot of setup/ multiple trash chutes, dumpsters, ECT. If you need a roof cutter only have to boom up once, only get one delivery. If there are dividing walls it will also eliminate wasting time tieing into the adjacent roof, just tear off the whole thing and do both sides at once.
Not sure where you are located but here in Philly the hardest part of city row homes is logistics, parking, trash, deliveys. We did 2 adjacent on a small narrow row last year, it was probably 1.25-1.5 the labor of doing only one, so made out great.