I want to update my Android.mk file in a package in order to build that new package, but I don't understand what the purpose of the
Using user tag is no longer recommended.
Add "LOCAL_MODULE_TAGS := optional" Then add "LOCAL_MODULE" value to PRODUCT_PACKAGES section of product makefile.
LOCAL_MODULE_TAGS defines in which build flavor this module should be installed.
Just give "user" tag, if you want the module to be installed in all of (user, userdebug, eng)
You can find full document here
eng This is the default flavor. A plain make is the same as make eng. * Installs modules tagged with: eng, debug, user, and/or development. * Installs non-APK modules that have no tags specified. * Installs APKs according to the product definition files, in addition to tagged APKs. * ro.secure=0 * ro.debuggable=1 * ro.kernel.android.checkjni=1 * adb is enabled by default. user make user This is the flavor intended to be the final release bits. * Installs modules tagged with user. * Installs non-APK modules that have no tags specified. * Installs APKs according to the product definition files; tags are ignored for APK modules. * ro.secure=1 * ro.debuggable=0 * adb is disabled by default. userdebug make userdebug The same as user, except: * Also installs modules tagged with debug. * ro.debuggable=1 * adb is enabled by default.