What are the advantages of shampooing twice?

Recently I’ve heard a lot about shampooing twice and doing a double-cleanse on your hair. I’m wondering if I should start this or not to help with my hair health - however, I have a little bit of a dry scalp and tend to pick at the skin under my hair a lot (I know it’s a bad habit), leading to lots of flaky skin. Because of this, I’m a little hesitant to try shampooing twice because I’m afraid it might dry out my scalp even more.

So should I start with the condition of my scalp? What are the pros and cons? Has it worked for you? Any help is appreciated.