Aren't you satisfied with answers you received in this thread
or in that one
As for your last question that's just a matter of personal preference, provided that you trust the package's provider.
As I trust Alien Bob and am a bit lazy I tend to install his packages instead of building them.
But I would build a package if I needed to set the configure options differently, for instance to get a feature not included in the package shipped.
To check you could type; "./configure --help" at the root of the source tarball and compare the output with the configure options in the SlackBuild.