I've written about NDA's over on Feld Thoughts - my most popular post on this is Why Most VC's Don't Sign NDAs. 

Today's post of the day is from VentureHacks and is titled What should I send investors? Part 3: Business Plans, NDAs, and Traction.  The whole post is worth a read even though the summary says it all:

"Summary: Don’t send long business plans to investors. Don’t ask for NDAs. Don’t share information that must remain confidential. Understand that investors care about traction over everything else."