There is discussion about flowers taking strength away from the growth of the tree so you should not let them flower more than once in three years. Well, maybe. I let them flower and every day cut off the blooms that are finished blooming. I think the tree then doesn't put any energy into seeds, etc., and maybe gets frustrated that it can't produce seeds, so has more flowers to try again. I may be anthropomorphizing a little too much.
The hummingbird sticks its beak way down into the flower and sometimes the branch seems to shake a little, maybe from the hummingbird, maybe from the wind. I don't see anything else it does. If it harms the flower, that would just encourage the tree to produce more flowers. A good thing.