Do Multivitamins actually do anything?

I’ve gone back and forth on taking a multivitamin since I know my diet isn’t all that great. Ideally I should be working to improve that diet but let’s say due to certain circumstances that’s a bit difficult at the moment.

Would it be worth taking a 1 a day multivitamin to at least correct some possible deficiency or is it very unlikely that it would have any effect?

Not asking for professional medical advice or anything, mostly looking to see if anyone else is taking a multivitamin and if so why?