I'm okay with most of the above comments, but I'd happily argue until the cows come home that 'plants will grow better in sand'.
Some might and, even then, only if certain conditions are met.
In one of my tanks, I created a sand 'beach', because I'd been told how much corys 'need' sand and that it was 'essential' for them to thrive. I used a long, suitably deep rock, to make a barrier and the beach was created. The rest of the substrate is ye olde traditional, river-rounded gravel.
My 9 Pygmy Corys will visit the beach on occasion, but they spend the rest of their time elsewhere.
With my second tank, I created similar barriers and am trying Tropica Aquasoil at the back of the tank, to see if its as good for plant growth as I was led to believe. The rest of the substrate is Argos Play Sand, purchased for my kuhli loaches.
Whilst the kuhlis are obviously content atop the sand, they also like to burrow around the plants, repeatedly uprooting them, as the plants in sand are slow at growing their anchoring root systems.
Note that this is not an issue for the plants in the gravel or Aquasoil.
Beach area in Tank 1.
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Tank 2
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Curse that wascally wabbi...kuhli loach.
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