It does have a use other than it's primary one, that can work in your favour too. I've never tried it, but apparently if you have serious carb ice or other carb related power failure, it is possible to keep the engine going by gently pumping the primer to feed it fuel.
SS
PS .... The reason I've never tried it is that IMHO it is an action very much reserved for dia emergency use only! Normal engine failure over landable fields is not such a dia emergency and 100% focus should be given to putting down, not playing with dubious remedies ... Over the channel and running out of ideas may induce me to try it though!
SS