You don't have to do that if they are stressed relieved fully during the build. Over the last 12 years I have found that's what sets us apart from just about every other builder. Even the ones who build purpose built machines to try and automate it. We just do it better.

But yeah if a builder tells you that you have to bring it back and they see pretty unilateral tension changes then they didn't stress relieve hard enough for those spokes and rim combination. It's not something to hang a builder for but that's what causes it to drop. Over the super long term rims can settle even more if they are carbon. On some there are just small moves most likely in the micro level that amount to just enough compaction to drop the tension slightly. This is after a year or two of riding.