The problem with a course at a time
Picking courses individually means every decision is made by the person with the least information about the subject — you, before you have learned it. The predictable result is three overlapping introductions and no intermediate material.
A path fixes the ordering problem once. It also makes the gaps visible: if step three assumes SQL and you have never written a query, that is obvious before you start rather than four weeks in.
How to use one properly
Follow the order, but do not treat it as sacred. If a step is too easy, skim it and move on; if it is too hard, the path will usually name the prerequisite you skipped. Finish each step's project before moving to the next — that is the part that converts watching into knowing.