This is still common practice. A better method that we use is two single pole switches wired in such a way that if either of the two switches is turned on, the fan would run.
The one switch would be located obviously in the bathroom, the second switch would need to be located at or near the wall thermostat.
This is a building code requirement, not a ESA or code book requirement.
The reason : Today's new homes are built more air tight then ever before. Because of this, building code requires some sort of "air exchanger" in each premises. More often than not, the bath fan controlled by these switches will be larger (90 or more cfm) compared to the other bath fans on the premises which are usually 50-60cfm. The large fan will most likely be located in the central or biggest bathroom of the residence.
If the home owner decides to get a proper Air Exchange unit (HRV), then the double switch requirement is exempt in the Ontario Building Code.
My 2 cents, I think this is just a band-aid solution to having a proper air exchanger in a house. I haven't met a single homeowner who regularly uses this method. If anything, I get numerous calls from homeowners asking me what this switch is by their thermostat and what it controls.
Hope this helps!