It is a good option but not essential. I’ve always multisown some and change the crops I do this with each year depending on the result I want. The rule is fairly straight forward that by growing some together closely you’ll get a greater number but they will be smaller in general as they share nutrients, light and water.
So it depends what you want to happen. If you want to grow lots of small carrots quickly, it’s worth doing. If you’d prefer larger carrots, space them out. Or, do a mix of both. Multi sow and thin out some of the smaller ones early on leaving the others to grow larger.
With carrots make sure they are covered with fleece to protect from carrot fly, which they will be more prone to being close together and thinning them will release the scent from leaves attracting them.
Other crops you can do this with tend to be most of the roots, beetroot especially, onions, leeks, turnips etc.