Preventing erosion of the substrate is one of the primary purposes of top dressing. I consider top dressing an essential part of the repotting process.
Many here do not use it, for reasons that I do not understand.
Great point. I’ve avoided top dressing because I prefer the look of the inorganic medium but I think I might start top dressing as a rule. I’m on a fifth floor balcony close to the lake and heavy winds will “pick up” pieces of the soil. Others may not be subject to this effect, of course.
OP: Top dressing will keep the soil in place AND promote water retention - which can be key in the smaller pots. Good quality orchid moss, lightly blended and poured/spooned on top, makes a decent looking top dressing. A level surface is key to looking neat.