Several functions are contained, that aim at making clean m-scripting much easier. E.g. an incoming argument of an m-function should represent the path of a writable file. A truely clean check of this argument would require many lines of code and a lot of thoughts put into it. So such are often skipped completely or cut down to very basic checks with rather unspecific error messages, if any.
With the library you write a single call to a checker function and receive a boolean plus an error message string, if required, that describes the problems caused by the argument in detail and contains a formatting %s for the specific argument description (like '1st argument' or 'specified file').
Another part of the lib is made up of signal flow scripts. For model analysis tasks it is often necessary to know about the sources and sinks of signals entering or leaving a block. Sometimes across model reference borders, sometimes not, sometimes skipping over conversion blocks, and so on. The functionality coming with Simulink is rather basic and often not available to the programmer, but to the GUI user only.