Well, when they want plants and also want to limit algae, that tends to be where things get iffy. Some add nutrients in pots and cap with sand etc. But........this only works so well, some might be okay with the results, but plants will leach nutrients into the water as will any sediment.

Fish waste might be cycled well in the tank, but it does not take much to supply algae compared to the plants.

Reducing the light is a better solution, but many are not willing to address the light issue nor reduce it either.

You can still add CO2 to lightly planted tank also and help increase the plant's abilty to grow at low light.

I sort of liken the few plants in a tank example to a garden that's been plowed and fertilized, but the garden only plants 10 of the garden and expects the rest of the garden to remain weed free all the time. Then you go in and try and remove all the nutrients from the entire soil to limit the weeds but that affects the crops as well. The weeds are better adapted to lower nutrients and thus stick around while the crop suffers.

Floating plants are better options for such folks, water sprite is easy and can be floated or planted. In general, most sparsely planted tanks have looked poor, often replacing the plants every few weeks/months, whereas packed fully planted tanks fair much better.

They also look much nicer.
I'm not sure why so many fish hobbyists are scared of adding more plants.
I guess when you fail with adding one or two etc, then you think it's hard and do not want to waste your $$ if they all get covered in algae and rot.

They have all seen nicely planted tanks and often are intimidated, so they know they are possible and like them, they just do not know some of the basics.

You can just tell them with more plants= less waste is left around and more plants = less algae, only a few plants= more algae.

Something will grow if they add light, they have a choice as to what that is.............

Regards,
Tom Barr