How effective is the serum?

I have a question because I'm curious about using serum.

I am wondering if using the serum consistently actually has an effect on the skin.

My skin has been getting really dry lately, so I'm thinking of changing my basic skincare products. However, I'm not sure if serums are actually helpful for moisturizing or improving skin texture. Advertisements claim they are good for elasticity and brightening, so I'm curious to know what changes those who have actually used them have noticed. I also want to know if the effectiveness varies significantly depending on skin type, and I'm wondering if it's a necessary step in my routine. Please share your opinions if you have experience using serums.