Many of the decisions you make as a software engineer have a long term effect. These decisions, the ones you want to get right as much as possible because they can be hard to change afterwards, are what architecture is about. Keeping this all 'in your head' does not scale beyond a very small team and documenting these on a Wiki like confluence is as frustrating as futile. So why not keep these records, little pieces of documentation, with the source they are documenting? This has the additional benefit of them following the exact same history in your VCS as the rest of your code.