Why is my CUPS scheduler repeatedly being restarted?

In my /var/log/syslog, I see (filtered irrelevant parts out):

Dec 30 15:00:10 myhost systemd[1]: Started CUPS Scheduler.
Dec 30 15:13:11 myhost systemd[1]: Started CUPS Scheduler.
Dec 30 15:26:11 myhost systemd[1]: Started CUPS Scheduler.
Dec 30 15:39:12 myhost systemd[1]: Started CUPS Scheduler.
Dec 30 15:52:13 myhost systemd[1]: Started CUPS Scheduler.
Dec 30 16:05:13 myhost systemd[1]: Started CUPS Scheduler.
Dec 30 16:18:14 myhost systemd[1]: Started CUPS Scheduler.
Dec 30 16:25:41 myhost systemd[1]: Started CUPS Scheduler.
Dec 30 16:31:15 myhost systemd[1]: Started CUPS Scheduler.

that is, every several minutes, systemd starts the CUPS scheduler. I don't see any messages about a failure, but:

# service cups status
● cups.service - CUPS Scheduler
   Loaded: loaded (/lib/systemd/system/cups.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since Fri 2016-12-30 18:55:53 CET; 2min 43s ago
     Docs: man:cupsd(8)
  Process: 30684 ExecStart=/usr/sbin/cupsd -l (code=exited, status=0/SUCCESS)
 Main PID: 30684 (code=exited, status=0/SUCCESS)

Now, /var/log/cups/error_log is empty, and /var/log/cups/access_log shows:

localhost - - [30/Dec/2016:15:27:21 +0100] "POST / HTTP/1.1" 200 186 Renew-Subscription successful-ok
localhost - - [30/Dec/2016:16:25:41 +0100] "POST / HTTP/1.1" 200 186 Renew-Subscription successful-ok
localhost - - [30/Dec/2016:17:24:01 +0100] "POST / HTTP/1.1" 200 186 Renew-Subscription successful-ok
localhost - - [30/Dec/2016:18:22:21 +0100] "POST / HTTP/1.1" 200 186 Renew-Subscription successful-ok

which may well correspond to restarts. I don't actually have a printer, nor a scanner, connected to this machine.

Why is this happening?