I find a grind more conveniant as I don't have to constantly reapply the tar as it wears off, and it works in the rain. That said (and because my new rim hasnt been ground yet), using tar does give you more choice in how much bite compared to modulation you want. I find smoother street type moves like manuals are easier with a small amount of tar, compared to a fresh and severe grind, where the brake tends to jar on the rim a bit. Although I remember the good old days when I used to buy it as liquid roof sealent from B&Q, paint it on, then have my pads stick to the rims on the edge of a drop... Oh the joy.