One of the reasons I like platinum printing is the ease of creating rough edges. Depending on the negative, I'll sometimes brush the sensitizer beyond the edge of the image area so that I can have dark brush strokes framing the image. For other negatives, I'll brush it on smaller than the negative so I can still have rough edges, but have them entirely exposed through the negative. It is entirely an aesthetic choice that I make on a per-image basis. Here are some examples.