On low power CPUs with integrated graphics, or even older phones, the performance gain from using turbo.js is going to be the the most obvious. However, all client-side parallel calculations can benefit from GPGPU - everything from image processing to geo-analytics. Technically, datasets for turbo.js could scale to multiple arrays, each with hundres of millions of values, but you're going to hit browser memory limits before ever exhausting the capabilities of your GPU.
Regrettably, some phone manufacturers choose to use older GPU models for their devices that don't support the required texture format turbo.js needs. That's why, e.g., turbo.js works on Samsung S7 models using the Qualcomm Adreno 530, but not ones with the ARM Mali-T880 MP12.