The following wording, from the setup script, is backwward
from the intended meaning, I believe:

Whether to enable debug information. Doing this will make PHP run
faster, but it will be harder to trace bugs. You are encouraged to
leave debugging on while PHP 3.0 is in alpha and beta state.

I think what you intend is:

Whether to enable debug information.  Answering "no" here
will disable debug information, which will make PHP run faster,

while making it harder to trace bugs.  You are encouraged to
leave debugging on while PHP 3.0 is in alpha and beta state.