Then you did it wrong. You should have just factored your thesis in multiple files, for example used one for each chapter.

That sounds like a workaround.

Actually, it is a pretty useful feature. I break my documents up into multiple files and can compile pieces of them together for different audiences. Want an executive summary of my research just build the abstract + a summary. Want to review the literature with my advisor, build the just the literature review.

However, I will agree that using it to address slowness of a build process is just a hack.

I suppose you would say splitting your C++ into separate source files is a "workaround" for slow compilation times, too? It could be, but both are probably good practice anyway.

It is, but you have to remember latex is best thought of a programming language that outputs pdfs so splitting into multiple source files is useful, as is source control.

My thesis was split in multiple files.

I agree that that aspect of LaTeX sucks. That said, as a matter of exchanging practical hints: If you haven't yet heard of \includeonly, you should definitely check it out ;)