How to interpret the article claiming NIST P-256 curve to be unsafe? Here: http://safecurves.cr.yp.to/ , I read that the NIST P-256 elliptic-curve is not safe.

The article lists several aspects (off-curve point, side-channel, etc.) where implementing P256 can fail the security, how should we understand these? 

I think this is valid for encrypting, but are these also valid for signing?
Quoting CodesInChaos:


  P256 is secure, it just lacks some nice-to-have features that make writing a fast and secure implementation easier.