I'm interested to see how others are approaching temporary users, eg interns or work experience users and licensing? Do you create a new account for each intern or use shared / generic accounts for them?

Each user needs their own account - no shared accounts. Also can mark as intern so others know e.g. Jim.smith.intern the same same you should be marking contractors e.g. jim.smith.ctr

Always a unique account for purposes of non-repudiation among other things.

We create accounts for each intern.  Those accounts are then deleted at the end of employment.  We only license a few things for all employees.  Most licenses are allocated on a "Must Have" basis.  If you don't need it, you don't get it.  One thing we do is if a particular software has a free "Viewer", a software package that allows you to view but not change the saved file from some expensive software, we will install that.  We find that many people want software "X", but they don't actually create with "X" they just review or read the content and don't need the expensive creation software "X".   A viewer application works just fine.

Always new accounts. Whilst yes a cost and time implication, audit and tracking in the case of an event of someone doing something stupid is always calming 

Treat them like regular users and buy SaaS that allows for flexible licensing and limited permissions. If you are buying inflexible SaaS you are probably doing it wrong. If you are not buying SaaS you are almost definitely doing it wrong. Slack’s licensing model is the perfect one for others to follow.