Observe the Release Train

The Salesforce four-month release cadence has become part of the community heartbeat. Salesforce is careful, but anyone publishing an enterprise-grade managed package will still want to do some form of regression testing against each new release.

Your choices are to (1) interlace Salesforce release testing with your own release cadence, or (2) climb aboard the release train.

Even if your release more often than October, February, and June [CMM], it still makes sense to sync up with Salesforce every four months.

All Aboard

If your customers maintain Full sandboxes, the Sandbox Preview window is an excellent time to refresh those sandboxes, and get everything up to date.

If you then run your own major release testing alongside your Salesforce release testing, you can be sure all the things work together.

Ideally, some customer sandboxes are not on a preview instance, so that you can also test your new version with the existing version. Since Salesforce stages its own releases, there will be a week when you have customers on both versions, and so your upgrade needs to be backwardly and forwardly compatible.