Hi I'm currently trying to install gtk 2.4 and having some trouble of course but my question is actually more general.

Having trouble installing freetype and fontconfig i googled and/or searched this forum and found that i need to pass --prefix=/usr to ./configure so that instead of installing to /usr/local it gets installed to /usr

so my question is actually when do we just do a ./configure and when a ./configure --prefix=/usr

also with gtk i read that we are suppose to do it with --prefix=/opt (haven't tried this, currently redoing the whole process from scratch)

thx in advance

./configure will use the default values for everything, and the default value for prefix may be /usr/local on your system.
In other words, typing "./configure" is the same as typing "./configure --prefix=/usr/local"
There isn't a specific time that you use one instead of the other, you would just use the --prefix argument when you want the program to be installed to somewhere other than the default location.