My opinions on Macro Algae
Pros:
They can look nice
Good food
Consume nutrients
Hiding place for bugs
Produce O2 and Consume CO2 when lights are on
Cons:
Some produce toxins
Yellow the water
Some can become invasive & kill corals
Too much can reduce waterflow and cause dead spots
Consume O2 and produce CO2 when the lights are out
If you pick the right species of algae for your particular application they can be a benefit. Be careful and do your research though or they can be a severe pest.