Lanayru Desert is covered with cacti. I realize they hold bombs at a nice height for the beetle to pick them, but do they have another purpose? You can bash on them and get the bark off, but can you destroy them? Do they hide anything valuable?
If you hit the red bulb-like object on top of the non-bomb cacti, they provide a heart. Besides this and providing bombs for the beetle, there isn't really much purpose to them.
The ones with blue tops have bombs, while the ones with red tops have hearts.
You can also use them to block the enemies with shells (can't recall their names), which should stun them.