USE flags
 

When I run emerge -p <whatever> gentoo prints a list of what would be installed, including Use flags.
Does this mean that portage knows which flags are correct for each package and will override any
default settings and whatever I have set in /etc/make.conf? If so, then why should I concern myself
with USE flags?

basically use flags define what other things that package would use at that time should you install it. those flags are a subset of all that package could do defined by what you have personally defined as acceptable flags for it to use. for example, if you install xchat without having the gtk2 use flag enabled, then it will be built without the gtk2 interface, only the text one. if you enable it, then the xchat ebuild will have permission to build the gtk2 gui.

Thanks for the input Acid Kewpie. Iknow what USE flags are for but was wondering if, having seen those specified for an ebuild by he output of the emerge -p <whatever> command, I have to change my make.conf file foreach individual ebuild, or if I can rely on the emerge operation to apply the correct flags, like for instance USE="flag" emerge <whatever> command would do. I assume yes but have learned not to trust assumptions.

there are a default set of flags defined, and each ebuild will use as many as are available to each ebuild. there is no "correct" flags to choose from. the ebuild says "I would like a b c and d" and your system configs say "i wish to use a b e and f" and so when you install that package you get it built including functionality for a and b only.