It is known that experienced summer residents before sowing seeds check their germination. How and why do they do it?

1) several dozens of seeds intended for spring sowing are placed on the bottom of a plate with wet leaves of blotting paper or fabric, and they are covered with similar wet sheets of paper or fabric on top; a plate with seeds should be kept indoors at a temperature of at least 20 degrees. Keep paper and cloth moist at all times.
2) Germination is determined in order to determine the density of sowing seeds.