It will cause problems once you have projects with internationalised names, on some platforms/browsers/app servers.

We have many support cases in Confluence because international URLs are used for attachment downloads, javascript and AJAX URLs, among other things. Most can be resolved with configuration changes (e.g. fix Tomcat URL handling, change Confluence response encoding), but it's an unnecessary problem when numeric IDs suffice.

Bamboo should use a numeric ID in all URLs, form submissions, etc. where identifying the project by name isn't necessary.