Mulch is insulation. It is a good idea to work your mulch into your garden soil. It is also a good idea to cover this with more mulch. Un-amended soil, which we ALL start with, turns to mud fast and dries to cement fast. ALL of us live on land that has been used by somebody else for 100-300 years, depending on where you live. You don't know if anybody has ferilized with anything there, so assume that Nobody has. Left alone all of our properties would grow tall vegetation, that would die back, That would create mulch and the cycle would continue next year.
https://www.motherearthnews.com/organic-gardening/gardening-techniques/garden-mulches-zm0z11zhun
By adding mulch where we want it we control where it goes. Remember, you can always use a bag mower in the summer (or rake up if you don't have one) and add that to your garden and that is free (minus the price of the gasoline.) Avoid doing this in August, which is when grass likes to go to seed. Leaves are another free mulch/fertilizer.
As you garden you study what the plants that you want to grow like the best and those conditions that your plants will tolerate. For instance, I love growing geraniums. I have 4 geraniums that I potted up before the freeze, which will kill them left in the ground. They can tolerate drying out by the roots and kept in a cool room, even a garage, then regenerate next spring. They are next to a cold, north facing window in one of upstairs bedrooms, drying out, bc they prefer that to overwatering, and they are all flowering. When I transplant next May, they will get lots more sun and Still flower for me.
Tomatoes would look like death warmed over in those conditions.
I bought a mini rose this winter that was pot bound in a 1 1/2 in wide and deep pot, so I transplanted it (to a 5 inch pot.) It really likes the top of my fridge, even though there isn't much light up there and I used recycled potting soil. Next May I will transplant in full sun and it will continue to flower as it is right now.
Some vegetables put down deep roots. Lettuce grows shallow roots and could really benefit from mulch so the roots don't dry out quickly.
Some people grow other vegetables, other plants and also flowers with their crops. I LOVE nasturtiums bc there are SO easy to grow and they spread out and partly smother weeds. I have studied and read that many people plant nasturtiums with their vegetables. You can eat the flowers, btw and the seeds are dirt cheap, buy them ANYWHERE. Same with marigolds. I am testing my older flower seeds this winter and will be growing as many as possible annual flowers to grow with my vegetables.
https://www.tenthacrefarm.com/flowers-in-the-vegetable-garden/
I have tried direct seeding and didn't have great success, so I am starting all annual flowers inside and transplanting this year.