The package presents subroutines and/or objects (along with a programming approach) which are independent of the GUIs that the programmer is targeting.
Dependence on a PIGUI can lead to project difficulties since fewer people know how to code any specific PIGUI than do a platform-specific GUI, limiting the number of people who can give advanced help, and if the vendor goes out of business there may be no further support, including future OS enhancements, though availability of source code can ease but not eliminate this problem.
There are some software developers who recommend this course of action, as it produces a better fit on each platform and eliminates the overhead often associated with PIGUI toolkits.
[citation needed] Obviously, this may require more effort in both the initial development and in ongoing maintenance (no single base of source code).
It also means learning how to code for every target platform, which is not (usually) a trivial task, hence the market for PIGUI packages.
Packages using a layered interface access native, third party, GUI-building toolkits to provide the look-and-feel compliance for each particular GUI.