How to reach out to profs at grad schools?

[Multicolormagic]

Hi there. I'm currently applying to doctoral programs in the humanities. I have heard that one unofficial step of the application process is sending emails to professors at schools whose research interests most closely align with mine. But here's the thing--I don't know what I should be saying in these emails when I reach out. People have told me to say something along the lines of "My research interests are X and Y, I've read from your bio that your research interests are also X and Y..." --But why should a professor want to get an email like this, what's the interest from their end? Is the purpose of reaching out to get a professor to basically agree to sponsor me in the application field? Is it just to get my name out there, so that when the professors have stacks of apps in front of them, they might recall my name and note that I expressed an interest in the program ahead of time? I guess understanding the reason behind this formality would also help clarify to me what I should be saying. 

I would really appreciate any help with this, thank you! I'm currently mystified. 

Edited October 25, 2019 by Multicolormagic

[Warelin]

17 minutes ago, Multicolormagic said:

I have heard that one unofficial step of the application process is sending emails to professors at schools whose research interests most closely align with mine.

Reaching out to professors in the humanities is not a requirement. Many have been accepted into schools without reaching out to professors at colleges. Reaching out to professors is more common in the Sciences because students often need to know if certain labs are accepting students.