Depends on the band and the desired goal.
For example, I'm mixing a 4 1/2 hour long concert for a two piece band (acoustic guitar and both members sing). Since the production is very consistent from song to song a single example is all that's needed for them to comment on the production.
Metal bands, that tend to want consistent sounds song to song are another example of mixing this way. Ultimately the client is looking for homogenous sounding tracks.
For more diverse artists sending them ALL the mixes is advisable because one song's mix may have nothing to do with the next song.
Another tip: when mixing "away" from the client I will generally make as balanced, middle-of-the-road mix as possible that leaves room for ANY element to get louder or softer, as well as have more/less top end, more/less mids, more/less bass, more/less reverb and so on. With the mixes I'll send them a questionairre asking if they want more or less volume/frequency/ambiance/whatever for each element of the mix.
That way you have room to maneuver mix-wise. It's always worked out great for me and resulted in a lot less "chase your tail" and a better finished product.