Procreate's selection tools are underused by most people I see drawing in it, and learning them properly changed my editing workflow significantly.

The freehand selection is the most useful. Drawing a rough selection lets you move, transform, or recolor a region without affecting the rest of the layer. I use this constantly for adjusting the placement of elements after initial placement.

Automatic selection (color fill based) is useful for flat-colored work — selecting by color fill and then applying effects or recoloring entire regions. For character illustration with flat color fills, this saves significant time versus painting over manually.

The transform tools inside selection: uniform scale, distort, warp, and freeform are all available within a selection. The liquify tool on a selected region gives you targeted distortion control. I use this for subtle proportion adjustments late in a piece.