Straight from the horse's mouth, so to speak: https://wiki.archlinux.org/index.php/Systemd/Timers#As_a_cron_replacement
An excerpt from the page above:
Benefits
The main benefits of using timers come from each job having its own systemd service. Some of these benefits are:
- Jobs can be easily started independently of their timers. This simplifies debugging.
- Each job can be configured to run in a specific environment (see systemd.exec(5)).
- Jobs can be attached to cgroups.
- Jobs can be set up to depend on other systemd units.
- Jobs are logged in the systemd journal for easy debugging.
Caveats
Some things that are easy to do with cron are difficult to do with timer units alone.
- Complexity: to set up a timed job with systemd you create two files and run a couple systemctl commands. Compare that to adding a single line to a crontab.
- Emails: there is no built-in equivalent to cron's MAILTO for sending emails on job failure. See the next section for an example of setting up an equivalent using OnFailure=.