Why should you start with thr lowest-powered objective lens instead of the highest-powered objective lens?

Answer 1

Two reasons:
1) You will find it much easier to locate things under the low power lens and then focus with a higher power in just that one area of the slide.
2) The coarse adjustment that you use for the low power lens is too much an adjustment to use for a higher power lens. If you tried to start with the higher power lens and adjust it you would end up breaking the slide and/or the lens while trying to get things in focus.

Answer 2

so you can see the whole thing and be albe to see what your looking at before you search for w/e your looking for