It will prevent the plastic layers from detaching too easily. Specially if you do the etching in a warm bath. If you do it right, the finish is far superior than using a marker, in particular edge traces that turn out very well defined. That means it's easier to do fine pitch SMD pads, for example.

Through the years I have done many PCBs using different methods: Sharpie markers, Posca pens, inkjet and laser printing, transfers of different materials, etc. Except perhaps for pro laser etching or routing, nothing beats photomasks. In my experience the quality I get with 3D filament compares to a DIY routing table, so if you have a 3D printer and don't mind chemical etching, you don't need one.