Why are there optimization levels (Noob question alert)

[richardcavell@mail.com]

Greetings,

I would like to ask why it is that optimizations are manually 
controllable to such a degree.  The way I see it: Debug builds 
deliberately include a lot of error-checking code that slows the code 
down and bloats its size.  This is undesirable in the 'release' 
version.  It stands to reason that the release version should run as 
fast as possible in most cases.  So how come there are degrees of 
optimization?  When would it be undesirable to fully optimize your code?

* Some optimizations are undesirable because they only work, or only 
work well, with a subset of the target architecture.
* Optimizations may increase code size, which is undesirable in an 
embedded environment with very limited memory space.
* Developers of gcc and hobbyists may be interested in researching the 
value of individual optimizations.

Are there any others?

Richard