The Band 4 reflects the best with vegetation. Yes there are differences in vegetational cover. It is easiest to see in band 4. 6. Cement, soil and rock are reflective. Landsat has a 30-meter resolution.
Water is the easiest to see.
Yes because the contrasts between are more noticeable. An advantage is that it makes some things become more obvious. A disadvantage is that it tends to cover up certain feature types.