With parametrized queries, that becomes a non-issue, but I still see no point in cluttering the database with data that's just going to be filtered out at some point - might as well filter it before it goes into the DB to begin with. The exception, of course, being those rare cases when some users need to see the filtered data and others need to see the raw data, but even then, you likely won't want to allow everything.
I am not sure if you are referring to the same sort of filtering mentioned in the document. The data is filtered before it hits the database layer, this saves resource being used.
No they're not. They're a method for ensuring that what is meant to go into some field in some database actually ends up there and does not start doing things it should not be doing.
Yes, but on the site, they make a clear distinction between parametrized queries with PDO and other types of input filtering. I misunderstood and thought you were referring specifically to the latter.
