Yes, I'd say so, but I'm not a veggie grower!

Yes, Hank, you can certainly warm up the soil by applying a plastic cover for a while. I do this to bring up the slugs, and cook any weeds, rather than for the planting. Spread loads of slug pellets, or you may have a scare when you lift the tarpaulin off!! A warm soil helps with planting, but not if new growth is bitten off at the top by any sharp late frosts!! Resist from planting out too early! If you plant into warm soil early, then fleece/cover the top, to protect new seedlings coming through. You can drop a pot over plants to protect them at night. Perhaps you would be better off with a coldframe to start your seedlings, then get rid of the slugs under the tarpaulin, and when temperatures are more ambient plant out. You will need to monitor the coldframe (box of wood with plastic/glass top) and open in the day with a brick or block of wood or similar so plants don't cook on sunny days.

I've never covered raised beds to warm up the soil.
Nature will do a perfectly good job for you. The time to cover soil of any kind is when you have planted early crops that can be affected by frosts with fleece, or cloches.

Agree Scrumpy ... as I said to Hank, I do this primarily to bring up the slugs, and kill off top weeds - better not use the word 'cook' or bilbo will be asking for recipes :-))))). Though thinking about eating weeds, and the FINAL revenge, I just recently found out that ground elder is also known as 'poor-man's spinach' and can be cultivated for the pot!! I am waiting with my knife and fork!!