Coffee is a good fertilizer for some types of plants due to the coffee containing a good measurable amount of magnesium and potassium which a lot of plants love.
The measurable amounts of magnesium and potassium help the plants to grow and thrive so by watering your plants with some coffee the plants can start to grow much better and be healthier as a result.
Just don't water the plants with too much coffee as it could kill the plants instead of helping the plants grow.
You can also add some coffee grounds to the plants to help them grow as well since some plants love acidic soil and coffee grounds contain acid that some of those plants love.
So you could water your plants at least once per week with a bit of coffee which is what I do with some leftover coffee in the coffee pot and I don't want to drink anymore for the evening.
I put it in a container and then use it once or twice per week to water some of my plants and flowers with and they seem to love the coffee like I do.
However you should still water the plants with water and only water the plants with coffee every now and then.