Slackware *.tgz packages are binary packages. Most distros you'll find have binary packages. But, with Slackware, you end up installing most everything from source, as there aren't many binary packages available for Slack.
Packages compiled from source can provide you improved performance benefits if you know how to specify compilation flags to optimize the software. But a lot of times, if you just do the ./configure && make && make install bit, then you might not appreciate much of a performance gain.