Outlining before starting to color or not

Hi! I’m a beginner and my main goal is do to thread painting, obviously nothing too realistic for now, but can someone explain to me like I’m 5 the use of outline?

I‘ve seen a lot of creators that outline their work before using color, either with a) a black outline or b) outlining with the color that section is going to be.

I don’t understand when I’m supposed to use the outline or not, and will soon begin my first work, so I’m not sure if I should start by outlining it or not. I understand is meant to make the images neater and hide any imperfections, but how/when do I choose to outline? Black vs color? How many threads?

I have also seen people using the split stitch to do this, but in my samples it makes the whole area look like a block with a border, instead of blending in with the overall design. Can I use another stitch, like stem stitch, or is there other way to fix this? I couldn’t upload a photo because my phone camera isn’t working.

Thanks! I‘ve seen some amazing work here and can’t wait for mine to be as amazing and the ones I’m seeing here 🧡