Personnaly, I used it a lot of time.
Firstly, you don't get any trouble by getting touched by plants or spikes, not that usefull but still.
And then, those Cacti (a cactus, two cacti) are really powerfull. Most ennemies dies after touching it two times. In the smalls area where the energy form projectiles are often losts, it is really usefull.
It can also provide protection when they are well placed.