Slow JQL can create multiple performance-related  issues:

• slow automation in JSD 
• slow down issue creation, assignment, commenting etc   JRASERVER-68174 if dealing with webhooks listening for these events 
• slow down kanban board loading

Just to name a few. 

It would be really cool if Jira ran a quick self-check on how long the JQL being saved to a board, webhook, filter, automation rule, to see if it violates the slow JQL rule of let's say 40 ms or something like that.