If you want to use a printer which is not a modern driverless IPP (AirPrint, Mopria, IPP Everywhere, Wi-Fi Direct Print, prints from smartphones) printer (then you do not need any Printer Application) and/or want to print in very high quality with many adjustable options, for example photos or fine art, then this is the right Printer Application for you.
It supports more than 3000 different printer models, especially inkjet printers from Epson and Canon, dye-sublimation photo printers, PCL 4/5c/e laser printers, but also some other printers. In addition it provides generic support for the different PCL flavors, everything which is supported by the Gutenprint CUPS Raster driver (http://gimp-print.sourceforge.net/). Some of these printers are probably also driverless IPP printers, but you can still use this Printer Application then as perhaps you could get better output quality. Note though that as a Printer Application is an emulation of a driverless IPP printer, using the printer's own driverless IPP functionality is recommended.
Gutenprint already ships for many years with most common Linux distributions (Ubuntu, Debian, Fedora, SUSE, ...) and has made many user's printers work and with this Printer Application these printers will continue to work in environments where only Printer Applications (and no classic printer driver packages) are supported.
Note: Gutenprint is an actively maintained project, therefore it would also be the correct way if Gutenprint gets turned into a Printer Application by its maintainers, or at least this be offered as an alternative to the classic CUPS driver. Especially they should create a native Printer Application, meaning that it does not use PPDs, CUPS filters, and CUPS backends internally. As soon as the Gutenprint project provides a native Printer Application, this Printer Application retro-fitting the CUPS driver will get discontinued.
This Printer Application emulates a driverless IPP network printer (IPP Everywhere) for each physical printer set up with it, so your computer's printing environment discovers it automatically and makes your printer(s) available for printing. Like on a physical network printer there is a web interface for administration, here especially also for adding and configuring printers. You find it with your browser under https://localhost:8000/. Note that currently printers have to get added via the web interface to use them. In the future, there will be utilities to easily find non-driverless printers and find the correct Printer Application for them.
With modern printers usually being driverless IPP printers, classic printer drivers, installed under CUPS by its web interface or a printer setup tool, are deprecated and replaced by Printer Applications (for the non-driverless legacy and specialty printers) which emulate driverless IPP printers as this one.