Disclaimer: I don't have that much experience, this is only my second year.

Last year, when I started, I put cardboard and then a layer of branches and leaves. Then soil on top. The soil layer was still quite thick (12-15 cm). This is inside a wooden garden bed frame to hold the soil. The ones I tried without the frame couldn't hold enough soil and I kept running into the cardboard when planting and the plants seemed also stunted. But the beds with the frame did pretty well. I planted a mix of perennials (strawberry, thyme, chives) and some annuals (carrots, lettuce, beets). I had another bed with tomatoes, basil, maybe cucumber along with thyme, lemon balm and oregano.

I didn't remove anything from the bed over winter. The annuals had been harvested or cut down at soil level (not dug out).

This year I found the vertical height of the soil reduced, probably due to some compaction and decomposition of the bottom layer of compost. There were earthworms in the soil. The reduced soil level allowed me to put some new soil on top. The perennials were still there after surviving winter. I planted some new stuff in the new soil (different from last year but still mixed around) and it seems to be doing well so far.

I am a bit weird in that I don't mind 'weeds' growing now and then, I mostly cut them at the soil level and use them as compost. I let some of them flower like buttercups, oxeye daisies, dandelions, yarrow and others. I'm only strict with invasives (I'm in Sweden so lupines are my nemesis for example).

If you don't have a lot of grass or weeds poking through you can skip the cardboard. Actually, I'm not sure the cardboard is beneficial at all. I mostly did it because I was trying to follow instructions. :)