Hi!
They give EXP too,but not to your main. They give EXP to your other ninjas if their level isn't the maximum. So they basically function as food.
I hope I could help.
~Spill~

thx for reply but tell me one thing ..its better to exp my main group in field and use food for other set ups ( ranked etc) or just save food for new nins that ill get later and would want to use in my main formation ?

Your main group should level as you do missions or sweep instances, hence no need to farm the field or give them food. You should only use food for new ninjas, or if you want to save the food, you can farm the fields.