Being an Atlassian Administrator and developer for 10 years, I've done a lot of JIRA Jira deployments, administration, managing and developing workflows.

This is ITIL stuff as Incident- and Change-management, Tasks etc. But also more special needs as a large CMDB, Customer, Subscription, Employee, License and Contract Databases. Internally in my Copmpany we use JIRA Jira for all sorts of thing, including being "mailbox" for a lot of the standard company mail-addresse as job@ support@ info@ etc etc; so we dont need distrubutionlists and all incomment mail are handled and tracked probably by an assignee.

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As an admin, You probably would know that Subtasks, defined as an issue bing a child of another issue (we will call it parent and child) - is an option You can select to disable in You JIRAYour Jira.

It can be disabled under Gear → Issues → Sub-tasks.

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As Subtasks only can live in the same project as the parent, it cant be moved to other projects, this is quite a limition for many companies that has different JIRA Jira projects for different departments/functions when subtasks are used for delegating work.

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Im sure that removing or disabling subtasks can cause fustration for hardcore and experienced users of Jira, so do always remember to argument and educate for the solutions You implement. Its all a matter of the way people work and are educated to use Jira ....

Real life story

Some years ago - Ive created a sub-task issue type called Sub-change