[iainmerrick]

Not really!

Exe size -- Sean usually includes a macro that lets you include the implementation only once (so you can use it as a pure header in multiple places, then as a definition just once).

Compile times -- if you use that macro, the implementation will be skipped by the preprocesser which is really fast.

Even if you build the whole code multiple times in your project, C compilers are also very very fast these days.

Many people follow Sean's style but use C++. That can be much slower to compile if you use fancy features. But if you avoid templates it's usually fine.

It's interesting that many big C++ projects are also header-only, but for totally the opposite reason -- they use templates everywhere so nothing can be compiled separately. That approach definitely does slow down compilation and increase your code size.