How important is it to stick to one or another?

I'm new to 3d and don't entirely understand the concept. I know that most models are done using quads which are later split into triangles for use in game engines.

Quads are apparently easier to split (4:2=2), while triangles are not (3:2=1.5) - so they might create artifacts. Now, I don't understand why would a triangle need to be split in the first place since it's already a triangle.

So I've hear to avoid triangles whenever possible.

On the other end of spectrum are people who claim that it's not a big deal and paying too much attention to making sure that everything is quads will hurt the model, because it gives you more restrictions to the modelling as well as takes you out of the so called 'zone' (it's hard to be creative when you focus on counting edges).

I personally like to keep my polygons a simple as possible with minimal amount of faces. If I have to add a vertex - I prefer to split a face and make a triangle, instead of splitting the whole polygon, but I'm not sure if that's a good approach.

What is your opinion and why? And how important is it in low poly modelling?