OSDev.org

I have realized that I use a #define'd system for configuration, the thing that's weird, is I have two of these flags in common with nearly every project I make..
one is
"LOW_MEMORY" which when defined will attempt to conserve memory at all costs

and then I got "SPEED_UP" which when defined will use potentially unsafe optimizations; also, it will attempt to do more caching and will optimize for CPU time fastness...this bascially doesn't go along with LOW_MEMORY, but anyway...

does anyone else do things this way for every project?

I sometimes do. I useually create #defines to help portability,
and create different modes (Debug, release). I sometimes
define COMPACT, which is simular to your LOW_MEMORY directive.

I use a DEBUG define when I need the code to print out a lot of debugging information.

DEBUG is quite common, Using defines for portability is also helpful..

Notably being able to add OS specific patches.. or workarounds for compiler versions etc..

Here is a handy site to find some common defines

http://predef.sourceforge.net/

Autoconf is one viable way to check what is and what is not available on a specific system..