tl;dr: Elements in a sketch should be consistently identifiable across additions/subtractions from the sketch to guarantee persistence to external references.
Maybe it is just me, but I rely a lot on 'layered' sketches. I draw main reference lines in one sketch and use them as external reference in other sketches. Now, if I redraw one of the reference lines or add/subtract elements in another manner in the reference sketch, the sketch that relies on the external references gets borked.
Quick example, start a new sketch, draw a rectangle, close it. Start another sketch, reference two parallel lines of the first sketch, close second sketch. Open first sketch again and fillet some corners. In the second sketch, references get altered, one is probably an arc now.
If I look at the naming of the references (f.i., Sketch.Edge4), it looks like elements in a sketch get renamed/reindexed from zero every time additions/subtractions take place. I wonder if that is an OCC thing or not...