Why does the first run of a profile take longer than subsequent runs?

By default, only new files and files that have changed are copied. This means when you run a profile for the first time, it will probably need to copy all the relevant the files from your source to the destination. However, on subsequent runs it will only copy files that have changed and so will be considerably faster. If it is a Fast Backup profile the first profile run will always take longer than subsequent runs.