personally in summer i like mine just a bit longer then normal.. just over the toe.. i wear thongs, or flip flops.. opened toe shoes mostly.. in winter i take the length back.. but i find that more uncomfortable then when they are long...
as far as clients go.. well most of my summer toe girls have no fe to speak of, so we don't have much choice.. but as we progress they are loving the fact that their toe nails are growing out and are asking to keep the length.
I have another girl who plays a lot of sport and she likes her fe shaped almond'ish so she doesn't suffer from ingrown toenails.. or get red blisters from when they bang in her shoes.