The problem it solves
Most people fail a training plan for scheduling reasons rather than motivational ones. The plan assumed five sessions; the week had room for three. By Thursday the plan is behind, and being behind is what makes people stop.
The planner starts from the time you actually have and fills it in an order that protects the things with the largest return.
How the week gets built
Available time is allocated in a fixed order of priority: resistance training first, because it is the hardest to replace; then easy aerobic work, because it is the easiest to accumulate; then anything harder or more specific, only if there is room left.
If you have very little time, you will get a small plan rather than a compressed version of a large one. That is deliberate.
Adjusting it later
Treat the output as a first draft. Run it for four weeks, then change one thing — usually adding time to the sessions you kept rather than adding a session you skipped. If you missed the same slot three weeks running, the slot is wrong.