Some educationalists think that non-exam art-based subjects can improve overall academic performance. I totally agree with them because these activities affect the brain positively for both short-term and long-term perspectives.
On the one hand, art-based subjects allow students to switch their attention and the calculative part of the brain has some rest and time to consolidate information. It has a really noticeable effect: studies show that students with creative activities have better quality of knowledge than students without creative classes (accuracy in tests is higher than control groups results and their level is sustainable over academic year). Also, this mix of cognitive rest and conditions for memorisation makes classes before and after art activities more effective both. It was shown by better academic results in research about different orders of school activities.
On the other hand, creative activities force the neural system to form specific kinds of connections and these improve intellect generally. Necessity of consumption of art such as music or paintings and its reproduction creates new ways of connections between already existing brain cells while creating new ideas supports neurogenesis. These factors make long-term structural changes such as a complex of neural nets that works like an optimisation algorithm in order to physically redistribute load that could be observed like non-conventional decisions with accounting large context of problem.
To sum up, art-based subjects help students improve their overall academic performance using a switching regime of brain work and physical impact on neural system patterns.