How to generate an installer package for Mac app?

There's also macOS Installer Builder, which is a CLI you can use to create an installer wizard for your .pkg: https://github.com/KosalaHerath/macos-installer-builder

Installers are great if you want various things to be placed in different spots – app here, documentation there, support files over here, etc. They're also great for providing configurability of the installation experience (optional extras), or hand-holding for an unusual type of installation that the user might not otherwise understand, or extra work (configuration scripts, permissions modifications, authentication, compatibility checking, etc.) that need to run during the installation process. There is nothing wrong with installers, contrary to the answer from @d00dle, although there is also nothing wrong with distributing your app through the App Store, or as a dmg.

For setting up your own installers, I highly recommend a program called Packages (http://s.sudre.free.fr/Software/Packages/about.html). I am in no way connected to it, but I use it to build the installer for an app that I work on. It greatly smoothes the process of making a complex installer, and has an excellent GUI interface.