I think keeping in the moisture helps in 2 main ways its that the soil does not crust . Second the absorbtion of water from the seeds by the peatmoss or dry soil! All I use is one sheet of clear plastic till the seeds sprout! Even in my sweat chamber my soil will crust because the chamber cover a large area and I notice the difference on flats that have now plastic cover in just a few days! Peat mixes will crust fast and pull the water away from the seeds just like a wick or a papper towel will absorbe water from any surface! The poor seedling is dried out and has no energy to break the surface even if its watered several days after crusting. That is my observance from the past!
The crusting will also suck the the juice from the seed itself through the small seed root emerging even in one dry night. I noticed this in a few boxed of new seedlings that never grew and when I looked at the seeds they had a small opening but were dried out!! Grass seeds grow better when they are covered with straw for that reason! Does anyone else agree with me?
I enjoy fishing ,gardening and a solar greenhouse! carpet installation repair and sales for over 45 years! I am the inventor of the Bobber With A Brain - Fishing Bobber!