When a new version of an ELF shared library (that we shall name L) is installed on the system, it's critically important that its Application Binary Interface (a.k.a ABI) stays compatible with the ABI of its previous version. That compatibility ensures that ELF binaries, that dynamically link with L, keep seeing the ABI they expect from that library L. Otherwise, if the ABI of the new version of L is incompatible of with the ABI expected by the binaries that link with it, subtle and sometimes hard to debug runtime errors follow.
As maintainers of a package that contains a shared library L, it's our duty to ensure that the ABI of new versions of L stays compatible with the ABI of its former versions.
Thus, comparing the ABI of the new version of a package against its previous version is critical to detect possible incompatibilities, review them and file relevant bugs upstream, should the need arise. That comparison should be part of the normal update process followed by maintainers of packages that contain ELF libraries.
Reviewing ABI changes in a given ELF binary
There are essentially two tools to review the ABI differences between two versions of a given ELF binary: