Nothing in the way of a stimulus is present to the body if the intensity of exercise is too low.
On the end of the spectrum- exercises such as running, though they increase the stimulus for positive adaptation, can increase the chance of damage and injury.
Harder work of muscles + shorter duration of activity= greater improvement and results.
You get better cardiovascular stimulus through an exercise you are able to perform for only 60-90 seconds rather than long periods of time. This is because the muscles, as well as the energy systems, are working harder.
You achieve a greater training effect if you put more effort into your exercise.
If you are able to engage, fatigue, and weaken muscle fibers within a defined time frame, then you are going to recruit all of the different muscle fiber types assertively- therefore getting the most mechanical and metabolic effort for producing an adaptation.
When an exercise is performed correctly, it eliminates all of the other extraneous components. This cuts down on excessive force and excessive wear and tear on joints.