I've discussed this on here before, and found that people don't seem to change their minds, whether for or against.
I am against the idea that exams have to mean doing only 3 pieces to death, and nothing more, and that they have to be horrible routines of scales etc without any fun. You can follow the basic syllabus for exams, and still do all the technique in fun ways, you can make the aural training far more general that just what is required for the exams, and include improvisation etc, and you can most certainly do many more than 3 pieces at each level. It's poor teaching that leads to the really restricted 3 pieces plus scales for a whole year experience.
I didn't do exams myself as a child, or only a couple on piano, none on my other instrument. I hated performing. I now kind of wish I had, in order to get me more used to it. But for piano at least, I followed the syllabus, doing a whole variety of pieces at each level, as well as the technique. It meant that I had to play pieces that I wouldn't have chosen, which was very good for me musically. I also had to do all the technical requirements that I might not have wanted to practice. On my other instrument, I didn't even do that, and I wish I had. I really notice now the lack of having good arpeggios and scales under my belt, and I have no idea how to get a piece up to proper performance standard, rather than just 'ok', good enough to move on, but not really special. Exams are good at focusing on really perfecting a couple of pieces, give some structure to what to practice, make you do new things that you might not like (I would always have chosen baroque pieces otherwise!), and make you do the technical stuff more than you might otherwise. I'd also have found it motivating to progress up the grades (wish there were more finely graded divisions actually), and have a structure to follow - that would have kept me practising more.
I also wish I'd had a lot more aural training. I found it hard for the exams I did, and even harder now as an adult coming back to do exams on a new instrument, and would have benefited hugely from singing/intervals/solfege, etc training at a younger age, alongside reading music.