Yep, I'm 100% positive I'm not sure & think it depends on situation.
Studies by Dr Bowker & others have shown the benefits of having 'packed' lateral sulcii & I know Dr Bowker has the attitude it should all be left regardless. But depending on climate, state of frogs, what's in there... it can possibly just form a better breeding ground for bugs. BUT then we also have to consider how even if we do clean hooves daily, the horse is still likely to get 'packed' soles soon after & for the majority of each 24 hrs, so what effective difference does the daily clean really make anyway.
I personally don't see my horses every day & don't clean their feet every time either & they either get thrush(gen in winter-early summer) or they don't. Doesn't appear related to how often they're picked.