When and how to use GCC's stack protection feature?

I have enabled the -Wstack-protector warning when compiling the project I'm working on (a commercial multi-platform C++ game engine, compiling on Mac OS X 10.6 with GCC 4.2). This flag warns about functions that will not be protected against stack smashing even though -fstack-protector is enabled. GCC emits some warnings when building the project:

not protecting function: no buffer at least 8 bytes long
not protecting local variables: variable length buffer

For the first warning, I found that it is possible to adjust the minimum size a buffer must have when used in a function, for this function to be protected against stack smashing: --param ssp-buffer-size=X can be used, where X is 8 by default and can be as low as 1.

For the second warning, I can't suppress its occurrences unless I stop using -Wstack-protector.

1. When should -fstack-protector be used? (as in, for instance, all the time during dev, or just when tracking bugs down?)
2. When should -fstack-protector-all be used?
3. What is -Wstack-protector telling me? Is it suggesting that I decrease the buffer minimum size?
4. If so, are there any downsides to putting the size to 1?
5. It appears that -Wstack-protector is not the kind of flag you want enabled at all times if you want a warning-free build. Is this right?