A trim for a horse that is going to remain barefoot is NOT the same as the trim done on a horse that is then going to be shod. Unfortunately, too many farriers trim for a shoe, then just don't put a shoe on. The basic goal of a trim should be to align the hoof capsule with the needs of the bony column housed within. It doesn't matter whether the horse will then have some sort of appliance attached or be left bare. A good trim can then be tweaked to accommodate either scenario.
A mechanically incorrect trim doesn't do the job well either way, and can actually be more harmful when an appliance is then attached because the hoof can no longer make it's own corrections thru wear. Many of the issues that are used as reasons for putting shoes on a horse - cracking, flaring, chipping, flat soles, underrun heels, stretched white lines - are due to the trim itself being mechanically unsound so the "problems" are just nature responding to the situation. Tighten up the trim and the issues begin to resolve. This doesn't rule out other contributing factors such as dietary imbalances and underlying health issues that also play a role so they must be also be recognized and dealt with or the feet will continue to be unhealthy, whether shod or bare.