Whatever the boss tells them to, har har!
Disclaimer: This post is biased toward Paralegals.
As a former Paralegal, I can give you some insight on this. Generally speaking, Paralegals are persons specifically educated (in either Certificate, or more commonly, 2 or 4 year college degree programs) to perform many of the tasks that an attorney performs, under the supervision of an attorney. At all times, a supervising attorney is ultimately responsible for her Paralegal's work product.
To be frank, some lawyers and law firms simply don't know what to do with a Paralegal, how to best utilize their skills. In my years as a Paralegal, I worked at various firms, each of which had a different use for my abilities. Sometimes Paras end up in unchallenging positions in which their daily workload is largely administrative, consisting of simple editing, writing letters, filing, copying, etc., and this can lead to boredom, frustration and job burnout. One wonders why they hired a Para, when a Legal Secretary could do the job. (This is not a put-down of secretaries, it is an observation that Paralegals are trained to perform substantive legal work, and secretaries are not. If you need lots of transcription, copying, filing, reception of clients, etc., and you are not comfortable with delegating your legal work, then you should hire a secretary.)
At the other end of the spectrum, there are some lawyers who maximize their Paras, and assign to them significant legal research tasks and legal drafting projects. Their attitude is, "take a stab at it", and a Para who has good legal research and writing skills can save an attorney quite a bit of time and time is money! Sometimes Paras are required to log a certain number of billable hours, just as attorneys are, and there is constant pressure to meet that billing quota. In this way, they are sort of like attorneys, but without the larger paycheck!
I have also worked with Paras who never seemed to master the legal research and writing basics, perhaps because this was not stressed in their educational program. This is another issue, the fact that the quality of Paralegal Education programs and standards varies. I was fortunate to have graduated from a Paralegal program that stressed the importance of legal research and writing, which are the foundation for the practice of law. The tools that a good Para can bring to a law firm are valuable and should be utilized.
These same skills helped me to get through law school. It was easier for me to navigate the law library and the online legal research sources and to draft various pleadings, simply because I had solid experience doing so. In my opinion, legal research and writing skills are absolutely the foundation of good lawyering. Sometimes lawyers themselves lack a solid foundation in legal research, so a knowledgable Paralegal could be indespensible to them, if they recognize and utilize their Paralegal appropriately.
If my practice grows to point where I can hire staff, I would choose a well-educated Paralegal (even without experience) versus a Secretary without hesitation. There is real value, in terms of their knowledge of legal concepts, and their ability to do tasks that can potentially save me time. And once again, when you're a lawyer, time IS money.