Reasons why I hate Save the Dates:
Pointless and waste of time
You can tell the modern guests via email/wedding website and the older guests (like your parents friends) through word of mouth. Good news is most people are internet proficient and those who aren't probably only expect official invitations.
Waste of money
Let's say you are sending out 100 Save the Dates. Let's also assume they are simple one sheet cards (i.e. small and light). You are already looking at $44 for the postage alone! If the cards are $1.50 each, which is towards the lower end btw, that means your total cost is already around $200 after tax.
Alternatively, you could do postcard Save the Dates. For 100 of those, you are looking at about $130 for cards, postage and tax (postcard postage is $0.29 each).
I will not be sending Save the Date cards whenever I get around to having a wedding. In my opinion, that is another $130 I could put towards my shoes. It is a very easy decision when you frame it by the question "shoes I get to keep or piece of paper that will go in the trash?"
Check out the USPS First Class Postage page for more details on mailing invitations!