First, basic terminology:

• cron(8) is the daemon that executes scheduled commands.
• crontab(1) is the program used to modify user crontab(5) files.
• crontab(5) is a per user file that contains instructions for cron(8).

Next, education about cron:
Every user on a system may have their own crontab file. The location of the root and user crontab files are system dependant but they are generally below /var/spool/cron.

There is a system-wide /etc/crontab file, the /etc/cron.d directory may contain crontab fragments which are also read and actioned by cron. Some Linux distributions (eg, Red Hat) also have /etc/cron.{hourly,daily,weekly,monthly} which are directories, scripts inside which will be executed every hour/day/week/month, with root privilege.

root can always use the crontab command; regular users may or may not be granted access. When you edit the crontab file with the command crontab -e and save it, crond checks it for basic validity but does not guarantee your crontab file is correctly formed.