Cow plants creep me out. I've mostly only had my Sims grow them to fulfill the Freelance Botanist aspiration and then they get sold or I let them die and use them for landscape decorations. However, they are good simoleon makers for financially disadvantaged Sims. If any of my Sims fish up a cowberry they don't need, I would have them take it home, plant it and then immediately go into build mode to sell it for 475 simoleons! They have to plant it first though to get that amount of simoleons.
Of course, this was before the gardening patch prior to Seasons when the berries were only worth 20 simoleons. I think they're currently worth 180. Not sure what they are worth after they've been planted now since I don't send very many Sims fishing anymore and kinda/sorta abandoned gardening after the grafting option was borked. *shrugs*