I was looking for some sort of process that is lagging my device. While searching I found that cron is running. If I understand this correctly then cron is needed to run serials of command at a dedicated time. Should I kill it or leave it? What will happen if I stop the cron?
In Unix/Linux systems, lots of OS background tasks are run as cron jobs. To see what won't run if you stop the cron daemon, type these commands:
ls -la /etc/cron.hourly ls -la /etc/cron.daily ls -la /etc/cron.weekly
If you really know what you are doing, and you are quite sure you can deal with the consequences, only then shut down cron.
Here are my Raspbian Buster system daily tasks:
-rwxr-xr-x 1 root root 539 Tue Apr 02 2019 22:13:44 apache2 -rwxr-xr-x 1 root root 1478 Tue May 28 2019 15:40:29 apt-compat -rwxr-xr-x 1 root root 314 Wed Feb 13 2019 17:40:39 aptitude -rwxr-xr-x 1 root root 77 Sat Feb 16 2019 11:10:23 apt-show-versions -rwxr-xr-x 1 root root 355 Fri Dec 29 2017 09:02:08 bsdmainutils -rwxr-xr-x 1 root root 1187 Fri Apr 19 2019 03:14:13 dpkg -rwxr-xr-x 1 root root 4128 Sat Jul 20 2019 12:35:58 exim4-base -rwxr-xr-x 1 root root 377 Tue Aug 28 2018 23:21:11 logrotate -rwxr-xr-x 1 root root 1123 Sun Feb 10 2019 12:11:20 man-db -rwxr-xr-x 1 root root 1403 Thu Mar 21 2019 22:42:36 ntp -rwxr-xr-x 1 root root 249 Wed Sep 27 2017 17:45:23 passwd -rw-r--r-- 1 root root 102 Sun Jun 23 2019 18:49:01 .placeholder -rwxr-xr-x 1 root root 383 Sat Mar 30 2019 17:10:38 samba -rwxr-xr-x 1 root root 441 Sat Apr 06 2019 08:18:26 sysstat
Also you can see in your system log what cron has been doing for root by doing this:
cat /var/log/syslog | grep CRON | grep root
Cron is a lightweight process that doesn't use a lot of resources by itself. Plus many other things assume cron is there and working. Leave it there.
atop for diagnostics. When the atop service is running, it periodically logs the machine's state to a file for later debugging.
I think atop defaults to every 10 minutes, but you could drop this significantly to help identify what processes are consuming CPU/IO/memory by stepping-through some top-like screens.
One of the scripts, which cron.daily executes is logrotate. Logrotate does archive system logs and deletes the old ones. If you disable cron, log files will eat all space on SD card. In Raspbian Buster logrotate is now driven by systemd daemon, so logrotate and few other cron scripts do not make trouble to disable cron.