Some plugins are still not E_STRICT safe. While debugging WordPress sites that may block you from finding bugs you are trying to find due to headers already being send.
Place this in your mu-plugins folder to disable E_STRICT warnings while debugging:
https://gist.github.com/daankortenbach/8538984
Fixing the E_STRICT warnings is of course the better option but so many exist, even in very popular plugins like WooCommerce.
OSX users may encounter a problem trying to disable the strict warning if using MAMP with PHP 5.5. There is a configuration problem that prevents strict warnings from being disabled. This should work for everyone else. Thanks for the tip, Daan.
Thanks for your comment Steven. I’m using this with MAMP Pro 2.2 and PHP 5.4.19 on OSX. I have no issues although I haven’t tried adding ~E_STRICT in the MAMP settings.