If you are a beginner I recommend you go buy Poolology for like $5 or $10. This will speed the learning process so that you will eventually know when the shot is on just by looking at it. Advanced and certainly professional players don't use aiming systems (they may use a pre shot routine that they think is their aiming system, but it isn't). They just know when the shot looks right based on hours and hours of play. Sure, for certain shots on occasion we all probably use one kind of reference or another, but for the majority of shots you will just start to see when it is on.
The problem with most aiming systems is that they make claims that are not based in reality. Sure, you can pocket balls here and there with just about any aiming system, but you will only have consistent success when your brain learns what correct shots look like, which ironically may require you to deviate from the aiming system in order to make the shot.