i guess that depends.
In terms of the plants...if you are doing EI method for dosing ferts; which will require you to "reset" your water. Also if you are using RO in lieu of tap, you would want to monitor your pH since you might need to boost GH or re-mineralize your water. This ecomes even more important if you are injecting CO2 wherein the buffering capacity of your RO might be close to zero.
In terms of fauna, it depends on how stocked is your tank. My 20L for instance is overstocked 175% of my filter capacity. This will require major waterchanges on my part for the health of the fish. Check out aqadvisor.com, it may help you inform what you decide to do.
If you were trying to go low tech "el natural" walstad, wherein you are relying on the waste and respiration of your fauna to provide the necessary nutrients for the tank, then you would have to match the plant mass (as the primary bio filter) with the waste/respiration generated by the fauna, etc. if you achieve this balance, then in this case you wouldn't have to change your water for 6 months.
In terms of plants, I find that waterchanges contributes more to the "look and clarity" of the water/conditions in your tank rather than what your plants actually require (dosing fert dosing aside)
In terms of fauna, I find that waterchanges can only be positive because it ensures a utopian like environment for the fishes. Frequent waterchanges eliminates the possibility of other bad stuff to develop that can harm your fish (spikes in water chemistry, ICH strains, etc.).
For my own tanks I am doing 50% waterchanges every week primarily to reset nutrient levels/GH in my tanks. Basically I find that my tanks look much cleaner with the waterchanges. The only drawback is its a lot of work, but if you miss a w/c here or there, as long as filtration is at capacity (mechanical or not) I don't think the inhabitants don't seem to mind either way.