[nwrep]

but on the hoof, how much can it matter?

It can matter a lot. The process of repair (nails, sowing it up, etc.) has to be carefully done, or it causes problems of its own, especially on thoroughbreds. It will for sure increase the odds against him from 1-5 to 4-3 or something like that.

[Pharmboy]

Thanks to both of you for the responses.