There are several reasons: 1. Unoptimized builds tend to be excessively large. LLVM's opt binary (citing this because it's something I have easy access to) is

There are several reasons: 1. Unoptimized builds tend to be excessively large. LLVM's opt binary (citing this because it's something I have easy access to) is 30x larger on an unoptimized build than an optimized build. [I think Rust is even worse than C++ at the unoptimized/optimized size ratio] 2. Debugging information is also excessively large. It's not counted in the above statistics I gave because I use split debug information (which keeps it out of the final executable for easier linking), but you're looking at debug information being a significant fraction of code size--maybe half of the total binary size could be debug information. 3. Because you include the build directory, you're carrying two copies of everything, minimum--both the .o files and the executable they link into. For a rough comparison of LLVM, the llvm source directory I have is 1.5G, the optimized release build I have is 15G (of which 1.7G is the actual binary executables), and the unoptimized debug build I have is 86G. Of course LLVM is unusual in producing a very large number of statically linked executables. 4. One of the dependencies inside clap is the procedural macros stuff (specifically, quote/syn crates), which basically requires building your own copy of the Rust parser. If you drop that dependency, the build directory sizes should be far, far smaller.