Customizing an Ionic app using SASS can enhance its appearance but may also lead to syntax errors that disrupt the build stream. The article demonstrates how a missing semicolon in the SASS file can cause a syntax error and break the gulp build stream, highlighting the inconvenience this poses during app development. To resolve this, the solution involves modifying the gulpfile.js to include an error logging option in the SASS task, which logs errors to the console without breaking the build stream. This adjustment allows developers to continue working on SASS files while receiving notifications of syntax errors, thus maintaining the functionality of the live reload server.