I tend to prefer working in real world units that is I always try to model to scale. This way if you share the model or import multiple models everything is the correct scale. If I was to change scale I would tend to do it across everything I model for the same reason.

One thing I have learned in Maya is that I just work in the default units of cm. The reason is that if you change the units it can make things like bevel go crazy. The reason is that the default bevel (which you cannot change) is .5 unit. So in cm you get a .5cm bevel and if you are beveling to create an edge to catch the light that is usually 1mm or less. So .5cm is only 5x what you'd want. Now change the default unit to inches and you are getting a .5in bevel which is almost 13x what you'd need for a light catching edge bevel. Now consider feet and your model literally looks like it has EXPLODED when you bevel as you are going to get 6 inch bevels which is over 130x what you would need for an aggressive light catching bevel.

I have tolerated this behavior on a couple of builds but in the end I just realized it's easier to convert to and work in cm and to scale.