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Like some of the other posters, I have attended Mr. Bond's excellent Unsharp Mask Workshop. If you are seriously interested in the technique it is worth the time. I'm sure you could call or write him and ask any questions about the workshop.
The two primary benefits of unsharp making are: 1) enhanced local contrast particularly in the shadows where it is needed most and 2) an increase in perceived image sharpness. These effects are a direct consequence of the edge enhancement that results from the density difference distribution between the negative and the mask (weak positive slightly blurred). This intensity of the effect is controlled by mask density and mask blur. The B&W technique was adapted from a color printing method where it is almost always required.
While it's true that for a given B&W negative, printing with an unsharp mask requres a higher paper conrast to get the same tonal result (this is because the overall constrast of the negative/mask combination is less than the negative alone), it is not true that it always requires something as great as grade 4. In fact, if you expose and develop in anticipation of using an unsharp mask, you can employ BTZS techniques to target for grade 2 or 3 or whatever you prefer.
Other printing techniques cannot yield similar results because they cannot reproduce the local contrast effects.
The term "edge effect" is often used when talking about image accutance and film development. While the concept is the same, the edge effects from unsharp masking are at a scale that is much larger by comparison, produce more noticeable results, and is far more controllable.
Just like its digital (and generally more familiar) counterpart, optical unsharp masks can be overdone resulting in prints that seem to buzz. If you like that effect then more power to you. But the technique can also be used tastefully in the traditional fine print and even someone familiar with the process would be unable to detect its use.
Unless he has changed his preference, Mr. Bond uses TMax 100 or Tech Pan film to make his masks. I prefer using Ilford Ortho Plus because it is much easier to handle in the darkroom (I can work under red safelight). I can make a mask start-to-finish-ready-to-use in about 15 minutes. If you are already familiar with techniques needed for BTZS, you will find the process easy.
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