1) Don’t want to narrow subjects down
The IB is perfect for the all-rounder looking to keep options open. Just make sure to take into account university course choices when choosing what subjects to take to higher level.
2) Aspirations to study abroad
Since the IB is studied abroad, it is recognized abroad! It is not tied to any one nation’s changing curriculum, so it is very easy for universities abroad to make offers for it.
3) Want to have an edge over other students
If you’re aiming for a top tier university, all other factors ignored, the IB is probably considered better than A-Levels.
…Or why traditional A-Levels might be better
1) Specific interests and skills
For someone who knows what they are interested in, the breadth that the IB offers may not be necessary. It is of course still very possible to be a competitive candidate with A-Levels, especially as they can be supplemented with things such as the Extended Project Qualification and extracurriculars.
2) Style doesn’t suit
The IB requires a lot of independent study and strategic organization to deal with having all the exams at the end of Year 13. It may be that this style doesn’t suit some students, and A-Levels will be more conducive to academic success.
3) No suitable IB school nearby
One practical consideration is that there may not be any IB schools nearby, or the ones that nearby do not offer the desired subjects. See this page on IB schools to check.