Speaking from personal experience in the workplace and at home, I would say it depends on your infrastructure and the needs.
At $DAYJOB, we have a number of critical servers providing critical components to business offerings to partners and such running on older 14.04 and 16.04 machines, and a handful of 12.04 ancient servers. These systems are temporarily being covered by ESM to ensure security updates and patches, howeover this is NOT a replacement for fully updated systems. Myself, the IT team, etc. have all been working to replace these outdated systems. While it's good to have security patches, ESM was designed with the intent of allowing 'some' leeway for patching, etc. for ongoing security support for a specific system, however it's only until you can find a replacement or migrate your systems off to newer versions of Ubuntu.
It was never designed as an 'end all' solution for when a release goes End of Life - and never will. It's designed as a stop-gap measure to permit you to run 'legacy' systems with (limited scope!) security coverage, while working to migrate your systems to updated OSes or software systems.
Therefore, the moment that your system reaches end of standard support (16.04 lost standard support in April of 2021 and ESM started then), you are in ESM support, and need to pay for Ubuntu Pro (previously branded Ubuntu Advantage for Infrastructure) to allow ESM entitlement per server in your environment (1 VM = 1 server).
Your primary goal regardless of Pro/ESM however is to migrate your systems off of legacy unsupported software and get them to a newer OS environment.
- Case in point: We just did that with four Python-driven API endpoints at $DAYJOB because we needed newer functionality unavailable in Python 3.6 (the version on the system in question that was EOL/EOSS) and was available in newer Python. So we migrated it to a new 22.04 server. The Python worked flawlessly and we were able to integrate newer Python 3.10+ functionality and modules that required Python 3.8+ to work, thus enhancing the in-house written software.
All in all, it will depend entirely on your organization, however ESM is a limited backstop - a band-aid to allow you to stay on the 'older' server software while working to migrate the workflow to newer Ubuntu systems or alternative software solutions (if working with software that's no longer available for newer releases for instance).
