A lot of effort goes into the release of new versions. New feature sets along the roadmap are derived from user feedback. Many upgrades provide new components or features that have no compatibility implications. A few upgrades can lead to (correctable) compatibility issues such as the Python Scripting upgrade from 2.2 to 2.5, which for the most part, led to feature and language upgrades that were requested numerous times on the forums. Newer versions are always done with backward compatibility in mind as a strong priority.
All that said, I would recommend testing your environment prior to rolling out significant upgrades. There are a number of differences between 7.2 and 7.5. You can also do things like snapshots with Virtual Machines, backups, etc, so that you can easily roll back if you run into problems.
I encourage user reviews of pros and cons of different versions. Feel free to start a thread. I have seen a number of posts where users share their feedback about specific features or “gotchas”. Similarly, we appreciate user submitted bug reports and typically fix them by the next release. You will also find cases where you used to do something one way, then find out that a better, newer approach works better. Ignition provides many ways of approaching tasks. I believe that backward compatibility and upgrades are an area where Ignition shines.