Right time to till soil

I am familiar with how to test the soil if it is ok to till, but I have been told not to till way before planting time.
Reason being that the rain and whatever will compact the soil again before planting. Any truth to this?
Also am using a Mantis Rototiller which by the way is one of the few great purchases I've made in my life.

Yes the rain can pack the soil down and make it hard! If your tilling a spot to plant-id wait till your ready to plant in that spot! ;) Mantis tillers are great lil tillers arent they!

**If soil is tilled when its to wet it will clump up and will be hard to break down! !!!!!