levels of doctors/nurses/technicians/janitors

I posted the following question on the Steam Discussion board on Aug. 27th. No one answered it, so I am posting the same question here hoping to get an answer.

What is the advantage of hiring higher level doctors/nurses/technicians/janitors?
They gain their levels with their work experiences, but their skills and specializations seem to stay the same. Their salaries rise with level. If there is no advantage of hiring higher level workers, is it better to fire specialists, nurse specialists, master janitors, and master scientists, and replace them with lower level workers?
Is hiring an intern doctor and training him/her to have high level of skill to 100% better than hiring a specialist with a big daily salary?

Hi, the main difference are the salaries, a specialist that you've levelled up all the way from an intern will be less expensive than one you've hired at this level straight away.

There are some more nuances, the employees get a new skill when they reach a certain level (for example 2 and 4 for doctors IIRC), and the skills improve by being used, so you can have more control over what their specializations are. Plus of course a lot of players will like to see their doctors progress in general or when role-plying etc.

Right, so I don't see the advantage of having a specialist doctor. The second specialized skill is available at the fellow level. A specialist doctor has nothing better than a fellow doctor, except that they take more salary.
Anyways, thank you for your response.