u dont use the same soil , as the roots usually go thru the entire soil . so when u pull the plant , they entire soil should be removed like as 1 peice .
even if u rip out ur plant from the soil , there are still roots the were torn apart , and stuck in the soil . so by that those roots take space for the new plant's roots.
and ofcuz , what they said before , as the old plant use up the good stuff from the soil.