The ease with which they can be gained means they can provide much needed splash damage and debuffs in the very early game. However due to their poor Stat Growths, they have no place past the early game.
If they have Regenerate, they can use that to heal themselves.
They can use Lure to trigger an enemy encounter.
They don't produce anything, and rather than Breeding stronger Pheroly you should be replacing them with better units.
They can be sold for 100 gold at Medium size and for 300 gold at Enormous size. Every level above 1 additionally increases their price by 5%.
Seliel will offer one on her second and third meetings.