In R6, the only cron job set is zebra indexing job (which is in fact
not required).
Most of the cron jobs that you can set all concern emailing, so if you
don't use that you're not missing out. Certain types of emails will
even work without the cron jobs (after you install postfix). These are
included in R7 and up.
The only other thing is a nightly database cleanup, which is non-
essential. (Purging completed zebraqueue and emails.) I started
including this in R7.
As far as I know, the rest of Koha will function without the cron
jobs.
You can view the available cron jobs in /usr/share/koha/bin/cronjobs/
crontab.example and see what they have. If you want any of them, just
add it line by line into /etc/crontab, replacing $KOHA_CRON_PATH with /
usr/share/koha/bin/cronjobs.
--Mizst