Hello.
I have some experiences with roots. 
I’m a no dig gardener for 7 years, mainly with help of course mulch of seasonal leaves, hay and grass in places where slugs are not a problem.
No problems with planting seedling in course mulches, but i had many problems before i learned how to sow seeds in it. Thank you so much for compost method Charles, it made my gardening much easier this year, because i use only compost or leaf mold where i’m sowing and everything is so less complicated!
Beside covering ground my main goal is to leave as much roots in soil as possible – was inspired by Emilia Hazelip’s Synergistic garden. Some gardens i created with help of initial diging, most of them without.
So, here come the roots of brassica, i leave them in as i cut at soil level with big garden sheers at the end of plant productivity. Most of them resprout, which is fine, a bit of young spicy salad in spring time is nice. I harvest this and then plants are weakend a lot and don’t resprout anymore. You can imagine how much biomass and digging this roots do in soil for a gardener from spring to summer time, it’s amazing! There is also no problem planting or sowing right beside the spent plants.
I also leave all other roots inside soil, especially the ones i eat, hehe.
Aloha.