Obviously that question depends on your motivation, but one good reason is that it is a great way to learn how software actually works.
R makes it very easy to see the underlying R code (you just type the function name), until you get to a ".Call" or ".Primitive": from that point, it is effectively a black box.
But as most of Julia is written in Julia, you can easily inspect and understand how functions work, all the way down. Moreover, by using the @code_* macros, you can also inspect the various stages by which the code is transformed from high level Julia code down to the actual machine code which is running on your computer.
R makes it very easy to see the underlying R code (you just type the function name), until you get to a ".Call" or ".Primitive": from that point, it is effectively a black box.
But as most of Julia is written in Julia, you can easily inspect and understand how functions work, all the way down. Moreover, by using the @code_* macros, you can also inspect the various stages by which the code is transformed from high level Julia code down to the actual machine code which is running on your computer.