The cases where incident light metering might not give you what you expected is with pure white or pure black objects. Incident light metering abstracts totally from the reflectivity of the subject, but if let's say the subject is very very white, such a reading might place your subject in a zone of the characteristic curve of the film where you don't have much texture.

So when using incident reading with a "milk white" subject, you would close a bit more than what suggested by your light meter. That's probably more true with small format than with MF or LF where film retains more details in the extremes "zones".

That said, with skin tones incident light metering is the best thing because you don't have to worry about the skin tone of the subject: any skin tone will be rendered well.

On the other hand, if it's a model in a wedding dress you are taking pictures of, or with a pure white hat, than, as said above, some caution might be used and some compensation applied.


PS As ever when talking about precise exposure, what above is mainly true with slide film. If using negative, and especially B&W negative, you have ample overexposure room and you dodge/burn as appropriate during the printing stage.