There's lots of options when it comes to increases, decreases and their visibility. Lots of times, you want your inc or dec to be visible, or to add a decorative touch to your garment. Take a raglan garment, for example.
That said, there are left leaning, right leaning and other types of increases and decreases, some more visible than others. It's a matter of taste.
is a good site to see some different ones, with illustrations.
As to your untrimmed edges, you can always crochet an edge if you need it for stability.
Hope this helps!