You really end up just exchanging one set of problems for another. It's certainly possible to have a beautiful macro tank, but it's certainly not going to be a maintenance-free build.
-Macro grows, and sometimes pretty quickly. If you don't want to keep up with the gardening, you have to stick to slow-growing varieties, and many of those are hard to get, at least where I am.
-...and lots of macro is hard to get these days, especially if you're not in the US. I've been trying to source blue hypnea for months, but have essentially given up because no one has it in stock in Canada.
-If you want a macro-only tank, you're going to have to import nutrients from somewhere. Will it be from fish, and will those fish eat the algae and/or root it up? What are you going to dose, and how much? And what are you going to keep? Not all algae likes the same water conditions, just like not all corals can grow in the same conditions.
-What about your CUC for nuisance algae? Many of them will also eat your desirable species. I had some lovely halymenia and agardhiella growing in my Evo, but I realized one day that it had all disappeared in the space of a few days.
-I find halimeda more difficult than red algal species. Some days it looks great in my Evo...and some days it pouts and looks awful. My corals in the same tank all look pretty great, though. I'm also going to have to give it a trim tomorrow, as it's growing in some places I don't want it. Argh.
-Where are you going to put it? Halimeda has holdfasts, which is great for putting it in the substrate, but lots of other species are free-floating and will drift around if you don't affix them to something, somewhere.
I have macro in most of my builds, but I use the desirable pieces more as accent pieces and/or hiding spots for some of my more timid fish. I've just acquired a pygmy filefish, for instance, and it enjoys hiding in my halymenia.
