Ranked in these QuestionsQuestion Ranking
Pro Cgroups processes control
Systemd groups all processes by services using Linux's cgroups. Think about memory/cpu/tasks/IO/Net limits and accounting for any service.
Pro Login management out of the box
Systemd contains a daemon called logind which is used for managing user logins.
Pro Default for many popular distributions
Systemd is the default init system for many popular Linux distributions (Arch, Debian, Ubuntu, openSUSE, Fedora, etc..). It should also be noted that some of those distributions allow users to use a different init system if they want.
Does one thing and does it well.
Con Not UNIX-like
One of the main argument that people who are against using systemd is that it does not follow on of UNIX'S core philosophies. 'Do one thing and do it well', instead systemd represents a collection of dozens of tightly coupled libraries. With responsibilities that exceed those of a simple init system because it also tries to handle things like device management, power management, mount points, cron, encryption, syslog, network configuration etc...
Con Makes dependent products difficult to port
Software dependent on systemd. Becomes difficult to port to systems that lack systemd.