CS:GO: From Zero to 0-Day
    However, sometimes programmers forget to remove the debug symbols from the final binaries of the game. Programmers are humans, and humans make mistakes.

Delivering software with debug symbols - wether commercial or non-profit - isn’t a mistake. It is a decision for better bug reports, traces and convenience.Executables/libraries on disk file size will increase with debug symbols. The  kernel and loader will look at binary headers and load only what is needed for execution into main-memory. Kernel and loader will not load the debug symbols at runtime, they are useless for them. The debugger will look also at the headers and use them to load the debug symbols, which are need for backtraces.  
Therefore initial file read from disk will take a little  more time but the execution is not affected. Startup speed is usually influenced by loading of further resources, initialization and checks. So you will get a lot for some bytes on the disk.https://stackoverflow.com/questions/24117063/is-a-program-co...https://stackoverflow.com/questions/39222698/does-compiling-....Some people still argue that security by obscurity works and hide everything. I doubt that.