Understand Systemd basic.target after boot time

The question I have here is to understand basic.target upon booting my CentOS 7 server. A few things I think I know correctly about Systemd: * Requires=unit2 means some unit1 will only be activated if unit2 succeeds all the way * Wants=unit2 means some unit1 will be activated regardless whether the listed unit2 succeeds or not * After=unit2 means some unit1 will only be activated after unit2 is activated * Things in Systemd usually starts out in parallel * .target is mainly for "grouping" and "ordering" (see [systemd.target]) * In reality, basic.target must be activated (along with everything it required and wanted) before reaching multi-user.target (which is the default runlevel for a server) All right, I hope so far I am right. --- Now, looking basic.target:

$ sudo cat /usr/lib/systemd/system/basic.target

[Unit]
Description=Basic System
Documentation=man:systemd.special(7)

Requires=sysinit.target
After=sysinit.target
Wants=sockets.target timers.target paths.target slices.target
After=sockets.target paths.target slices.target

So now my interpretation is: 1. basic.target will only be activated **after** sysinit.target has succeeded 2. Furthermore, basic.target desires to have sockets.target and etc to be running 3. The additional After= means, okay, please only activate basic.target after sockets.target, paths.target, and slices.target are activated. It's okay for timers.target to fail. 4. Then why not combine two After= into one? Why not use Require= instead of Wants (except timers.target)?