Bread making, lightly oiled bowl covered, why?
The bowl is simply to contain the dough.  You can use any container you like.  Depending on the type of bread you are making, you often need to build gluten strength, this ends with pre-shaping and shaping.  Shaping matters at this point. With kneaded bread, the "ball" is simply an artifact of kneading or stretching and folding.  Covering reduces the chance of the surface drying out, and helps maintain temperature.  Oil in the bowl is not necessary in most situations, and is not part of "every recipe."