Soils that contain a lot of fine particles - especially topsoil and fine sand mixed with peat or compost, compact easily, 'squeezing' the air out of the soil and allowing water to take its place, which creates anaerobic conditions that kill roots or impair their function.

Generally speaking, the greater the amount of air your soil holds, the greater the potential for your plants to grow to be all they CAN be. The minor downside to these soils is you often have to learn to make your own and water a little more often, but the upside is it's MUCH easier to grow healthy plants, with a much wider margin for 'grower error' - PLUS it's cheaper.

If you'd like to learn more about the concept, just follow this embedded link.

Al