Need for Support Material

I just got a Flashforge Dreamer. I have tried it out with mostly success. I tried printing a geodesic dome in ABS with PLA support and the first attempt did not work. The dome had a radius of 20mm and each element was 2 mm thick. The default slicer generated support for the center, but not for the edges that are mostly vertical. I increased the element thickness to 3.33mm and tried again. By default, support material is not enabled. I forgot to enable it, but it worked anyway.

I have been thinking of designs that would make removing non-disovable supports difficult. What criteria can we use to determine if a part needs support?

if theres more than 1 inch from point A to point B use support, specialy in straight lines, it just happend to me, i printed a flat surface of about 80mm, i check the support function on slic3r but only added support for the sides, so i end up with a lot of hanging layers, noo preatty at all