Well, I'll admit that I'm a bit biased on this topic.... but here is my 2 cents.
Customers who buy S4S lumber are typically looking for perfectly clear boards - both sides and end to end. They tend to be interested in maximum yield from their boards. Therefore, lumber sellers who specialize in S4S lumber typically only pick clear boards for S4S, since that's what the customers are buying. But most logs will not produce 100% clear lumber (typically not even 50%). So that means that if you buy 12 S4S boards they most likely came from 8 - 12 different logs. That means that there will be some variances in color and grain amongst the various boards. If you're planning to stain your project a dark color, then no big deal. If you're more interested in the overall function of the project instead of seeking out and harmonizing the wood grain, also no big deal.
On the other hand, customer's who buy rough sawn lumber from us frequently are looking for log matched boards instead of perfectly clear boards. They will accept some defects in the lumber in exchange for being able to selected bookmatched boards from the same log. This can provide for better harmony between the individual boards in the project. More artistic customers will seek boards that have the character that they desire. They may buy a 12' long board because 3' of it has wood figure that will be in harmony with the design and location where they will use it in their project.
Here are a couple of different examples of table tops. In the top example, if you look past the defects you will see that the lumber is not color or grain matched. The thing that stands out are the individual boards, but there is no artistry or harmony between them.
Compare that with this glue up of bookmatched boards.
On the second tabletop you have to look much more closely to see where the boards were joined together. The color and grain match is very consistent since all boards came from the same log. What strikes your eye is the overall presentation of the entire glued up top - not just the individual boards.
Oftentimes lumber that has truly outstanding figure may have defects in it. Here is an example.
The photo below shows a surface checked board with a major side split. There is no way that this board would be selected for S4S inventory by most wood sellers because many customers would discard it due to it's defect.
However, below is a photo that shows what the bookmatched figure of this heavily defected board could be. Master NCWW artisan Dan O'Sullivan looked beyond the defects and saw the spectacular potential for the board. He bought it and brought it to us for resawing into veneer.
The photo's speak from themselves.
At the end of the day, buying S4S versus rough sawn may be related to what you're building (function versus form), as well as where you are at in your woodworking journey.
YMMV.
Scott