Genuine watches are built/finished better than reps. Also, rep watches generally come with used/unserviced movements, so unless you have your new rep professionally overhauled upon its arrival, its accuracy & lifespan may be limited. Further, contrary to many sellers' hyperbole, no rep that I am aware of is 100% or an exact copy of its genuine counterpart, which means that an astute collector will be able to spot a rep & ID its wearer as a poseur.
In my case, I tend to build frankens (watches that are constructed out of genuine spares or parts from various other watches) of watches whose values reach into the stratosphere & buy gens otherwise. For example, current prices for Double Red Sea Dwellers run from $25k-$40k, so I built a (gen-powered) franken. On the other hand, current prices for 80s Datejusts run around $4k-$8k, which is affordable, so I went gen.