IMO I think it's only polite to use mudguards on club runs.
i.e. the person behind you in the group doesn't get soaked by the rooster tail from yr back tyre!
SKS Race blades are reasonably easy to fit if you don't have eyelets and removable quickly if the weather's OK.
A full rear guard stops all that salt and grit going in yr front mech.
Also I still can't get commuting traffic grime out of my Addiscombe jersey.