configure tweaks for Makefile generation?

[Gary Aitken]

I'm confused about tweaking a Makefile which is normally generated initially
using ./configure.

If one needs to define variables which affect the make process,
and a Makefile is generated initially using ./configure,
is the right thing to do simply to insert the define directly into the
Makefile, or is one supposed to define the variable in the environment
and rerun ./configure?

In other words, should the goal be to make configure generate an
appropriate Makefile, or is configure just used to get a starting point
for an appropriate Makefile, and the Makefile treated as the source
from that point on?

Thanks,

Gary