Jira has no field level security, that means if a user has permission to view an issue, he can view all the issue fields including time tracking fields such as, "Remaining Estimate", "Original Estimate", "Time Spent". If your user base also contains your customers you may not want them to view how many hour you have spent on the issue, or your estimate fields. 

Starting with 2.25.0 release, WorklogPRO has capability to hide its time tracking related information from other users, such as "Worklog Panel" and "Time Tracking Panel". The add-on can also hide build-in time tracking information shown by Jira but this is not a 100% solution. A user with necessary technical knowledge may view time tracking information by using REST API of Jira or using some debugging techniques. 

This option is off by default and you have to enable it from add-on settings. You need Jira administrator permission to change add-on settings.

There are 3 different values for "Hide Time Tracking" configuration:

• Jira Default: Visibility of time tracking information is the same as Jira, any user who can view the issue can view time tracking related information.
• Users Without "Work on Issue" Permission: Time tracking information is hidden from users without "Work on Issue" permission.
• Groups: If you select this option, "Hide from users in Groups" field will be visible for you to specify User Groups. Users within the specified User Groups will not be able view time tracking related information.

When this setting is turned on time tracking related information will be hidden from following locations:

• Worklog Panel: This panel and contained worklog information is never send to the browser so this information is unaccessible by the users. Note that after installing the add-on there are two version of those panels, build-in ones from the Jira and the ones provided by the add-on itself. The add-on only hides its own panels, you are expected to disable build-in Jira panels after installing the add-on. Since this is add-on's own panel, hiding this information is more safe than hiding Jira's build-in panels. It is never send to browser of the user.
• Time Tracking Panel: This panel and contained information is never send to the browser so this information is unaccessible by the users. Note that after installing the add-on there are two version of those panels, build-in ones from the Jira and the ones provided by the add-on itself. The add-on only hides its own panels, you are expected to disable build-in Jira panels after installing the add-on. Since this is add-on's own panel, hiding this information is more safe than hiding Jira's build-in panels. It is never send to browser of the user.
• Time Tracking information in Edit Issue Dialog: This fields are actually added to Issue Dialog by Jira but, removed by the Javascript before the dialog is shown to the user. 
• Time Tracking information in Issue Navigator: This fields are actually rendered by Jira but, removed by the Javascript before the complete list is shown to the user. 
• Time Tracking information in Issue History Panel: Time tracking information is actually rendered by Jira but, removed by the Javascript before history panel is shown to the user. 
• Time Tracking information in Activity Stream: Time tracking information is actually rendered by Jira but, removed by the Javascript before the activity stream is shown to the user. 
• Time Tracking information in Jira Agile Boards: Time tracking information is actually rendered by Jira but, removed by the Javascript before the board is shown to the user.