People use both, for reasons of tradition, ergonomics, practicality, available toolset. Boldface is obviously common in places where BB is unavailable, more res

People use both, for reasons of tradition, ergonomics, practicality, available toolset. Boldface is obviously common in places where BB is unavailable, more restrictive, more difficult. Web publishing is a great example. BB is common, in my experience, in hand-written text where bold isn't really an option. It is, to my tradition, the most common and recognizable way to indicate the most common field sets and also generally is a good stand-in for any "large category" of interest. Bold is used intermittently in my experience, probably due to its inability to be hand-written. To me, it tends to mean "vector" or "matrix" much more than set. In hand-written forms, I sometimes see "arrow hats" instead, especially for vectors.