I don't see a problem; whether I'd do it just depends on the card. Where there are border markings I definitely will clean up a crappy looking cut that misses the mark if I am going to have it slabbed. I haven't touched this one but if I wanted it in a slab I would even up the edges so it looks nicer:
As an aside, it is interesting how many kids of past eras had no fine motor skills, even with a scissors.