I have been doing it with all of my egglings and hatchlings but I was always wondering something. Other than getting scales, what exactly does nurturing do??

egglings:
every six correct nurtures adds a bonus +1 to their maturity counter (meaning they'll hatch an hour earlier)

hatchlings:
every four correct nurtures gets them +1 maturity
every eight correct nurtures gets them +1 to their lowest stat (though mana only goes up if the pet has all the other stats maxed)

(obviously you cannot manage to get any of these boosts (save one +1 maturity to a hatchling) on your own- this is why you get other people to help with nurturing yours and help other people by nurturing theirs)

Theres also a very small chance of getting species essences to use to create pets in the Generator. I think from the time I first started playing up to now, Ive managed to get about a dozen or so.

And of course during the four annual fests and a few mini-events (the Week of Love, Lucky Week (or whatever the St. Patricks Day event is called), etc.), you get special event currencies & other things (Candy Hearts, Snowflake tokens, Decorated Eggs, etc.) from doing it.