I'd say you've answered your own question right there:
Originally Posted by
FedericoMena
The only times where I've wanted a bit more traction is with very muddy/soft ground, or with very loose and big gravel going uphill.
When slicks stop gripping it's time to get some tread, although depending on conditions you may be able to use a file tread or a hybrid tread with a center rib like the new Clement USH.