Common practice because it's the most common sold, loading up on Grapjuice and Meat.
Now, if I wanted to heal myself better than Meat, there's always buying Cake instead.
What's the Grapejuice equivalent of Cake?
What recovers SP the best?
Grapejuice just isn't worth the zeny it costs sometimes, it doesn't exactly recover "a suitable amount of SP" for me.