I mean, if you're already running decent code or already have extremely good tooling where small examples can be easily sent to other machines. Additionally, debugging code running on other machines is also a huge pain in the ass vs. being able to step through it directly, locally.

Almost all of my (and my lab's) time is spent tinkering with small numerical examples before sending it off to one of the lab machines to run overnight, and using the GPU on the MBP through OpenCL is a huge advantage.