It is important to note that if returning FALSE from this method, PHP will in turn output the following warning:
Warning: Unknown: Failed to write session data (user). Please verify that the current setting of session.save_path is correct (/var/lib/php/session) in Unknown on line 0.
This could cause minor inconveniences, however if the session should not be written as per design, then returning TRUE after handling (and not writing) the session will avoid further issues.
All in all, better return TRUE at all times except in cases of hard errors.