To trust built-in metering or to use external pro-exponomete

[A.B.]

A separate incident meter would be my first choice too and will be the most used meter; however I think that in several situations a spot meter is just as important so I would get a meter that has both as most in camera spot meters are too wide angled.
One example where a spot meter becomes indispensable is when photographing big interior halls like inside a cathedral or mosque. Usually the light intensity differs dramatically from one area to the other, often within just a few meters. This is because some areas are hit with direct sunlight from windows and others only get reflected light and the difference in light intensity is too much for slides and often too much for print too. You have to compromise and select the area you want to show details in and meter and compose accordingly.
Having an incident meter in this situation will have little benefit, since most likely you won’t be able to take a reading from the place you want to expose correctly (the ceiling?) and you’ll probably be standing in an area with completely different light intensity so you can’t take a reading there. Only a spot meter would do the trick.
Along the same lines, in long open ended corridors the light intensity drop from the open end downwards is usually dramatic and again hard to meter. A spot meter will let you expose for a certain arch that you focused on and composed your picture around.


------------------
A.B.

OasisPhoto.com – Images from the Magical Sahara.
ShortWheelbase.com – Jeep preparations.
Coordinates Converter – Lat/Long <-> UTM Conversion Tool.