Presently Bamboo allows cleaning of directory after each succesfull build. It will be a great idea to clean before builds as well. This has the added advantage of providing the following:
* debugging - as generated files could be easily inspected without resorting to artifacts * ensuring behaviour for aborted builds * takes care of possible nasty linking interference cases when a new build produces less files or a different set of objects than the previous one * generally when certain tools get confused about already existing files (or folders with the same name, etc.)