Compare the tone in these two sentences:
We can’t send your credit card until you send us your signed application form. (Negative)
We will send your credit card to you as soon as we process your signed application. (Positive)
Or these two:
Enclosed herewith for your perusal, please find a copy of my summary of last Friday’s meeting. (Formal)
I thought that I’d drop a note to you, Ms. Johnson, and thank you for the pleasant visit I had with you last Friday. (Friendly)