Plants absorb light in the red/ blue areas of the spectrum and reflect green, so likely not much self-absorbtion

One theory (“purple earth”) is that simpler now extinct life used to use retinal for photosynthesis which uses the most abundant color in the suns emission spectrum, green light. This left only red and blue light which other organisms evolved to use (now plants). Retinal is fairly unstable and thus those organisms needed to use tons of energy just pumping out retinal to co tinue operating, while chlorophyll is relatively stable in comparison, so those organisms had higher net energy intake even with lower energy available in the red+blue areas of the spectrum since they expended less on just existing, and were able to grow and outcompete the purple counterparts.

For advantage, not necessarily- it could attract pests or animals that eat or damage it, resulting in it dying faster.