Distributions such as Debian or Ubuntu conveniently create folders such as /etc/cron.daily, /etc/cron.hourly, etc, where scripts can be placed such that they are executed on a schedule. Running crontab -e in order to view the crontab, reveals that cron is using a script called run-parts in order to execute all scripts within such folders and "run-parts" specifies that scripts are run in lexicographical order according to "the C/POSIX locale character collation rules".
This allows users to organize folders such as /etc/cron.daily with scripts, say, preceded by numbers in order to establish some precedence. For example, here is a folder structure of /etc/cron.daily:
---+ etc
+
|
+---+ cron.daily
+
|
+--------+ 00-first
|
+--------+ 50-mid
|
+--------+ 99-last
|
+--------+ order-unimportant
|
+--------+ some-other-script
In this example, order-unimportant and some-other-script are scripts where the order of execution relative to each other is irrelevant (order-unimportant will always precede some-other-script due to lexicographical order). The scripts 00-first, 50-mid and 99-last will now run in the order that they are mentioned due to being prefixed with numbers in increasing order.