For Experienced Musicians
Having suffered through the experience of learning to read music, you should have a medal or a trophy, or maybe a Purple Heart. It is a daunting task, and not everyone is able to do it or be willing to stick to it. So there may not be any value to you in learning yet another way to read music. Once you've really learned a piece, you're probably not really reading every note and are mostly relying on muscle memory with the sheet music providing queues to jog your memory. However, I am aware of some who are in fact weary of struggling to learn every new piece because that means having to pay careful attention again to all the challenges of reading traditional sheet music notation.
So some experienced musicians might be open to find an easier way. Already knowing how to play one's musical instrument, makes it easier to focus just on the notation. Ideally, a simpler to read notation can be picked up relatively quickly and used as a "2nd language". If you would like to read a more comprehensive description of WYSIWYP notation, its advantages, and the overall project, read this description on the Music Notation Project (MNP) website. The MNP is a community of alternative notation designers.
There are also some special occasions where a musician might want to use WYSIWYP such as learning a musical passage that has complex rhythms. For these, it may be helpful to be able to visualize the time relationships among notes on the same and different staves. Syncopation in particular may be one of those cases. After mastering the passage to the extent of being able to play it with muscle memory, the musician could return to the traditional sheet music.
The following shows a straightforward 5 bar example of syncopation on a single staff. It's from an online tutorial on how to read traditional notation syncopation.
The blue arrows on the 3rd and 4th measures indicate the beat, while the red arrows indicate the syncopated notes.
Below, WYSIWYP indicates both beat (via measure bars and beat tics) and notes relative to them on a timeline. This provides a visual and intuitive representation of the relationship between beats and notes. It's easy to see that the notes do not line up with the start of the beat. It's also clear that, except for the final whole note, all of the notes are the same duration even when crossing a measure boundary.
In this next more complex example, there are both treble and bass staves. This snippet was captured from a dynamic playing of the notes during the tutorial so just look at the middle two full measures 6 and 7. The time signature is 4/4.
With WYSIWYP, the musician can see how the notes relate to one another on different staves. This notation untangles the ties and dots on the treble staff above to reveal that the tied notes are simply equal to the length of a full beat, although not aligned on the beat. In addition, it can be seen how the start of the notes on the treble staff line up with the 4th note in each beat on the bass staff. (This image corresponds to the full measures 6 and 7 of the traditional notation snippet above.) And, it's easy to see there are 4 beats to the measure.
By the way, WYSIWYP doesn't "do" time signatures, so the treble notes here are called one beat notes instead of quarter notes. And the tic marks visually demonstrate the score has 4 beats to the measure.