I never understood this: in web design whe[nre] will it seem sensible to fetch results 1 by 1?

I am talking about, why must I personally use [cde] after i may use [cde]?

PDOStatement->fetch*() will fetch all of the results into one large array.

With large result sets, it might exceed the PHP script's memory limit.

A pure PDOStatement->fetchAll() will fetch each record 1 by 1, overcoming that danger.

This is the only reason to not use fetchAll() I'm able to think about.