Only uploading and downloading files is. When you FTP, please connect, upload your files as quickly as possible and disconnect from the server so that others can upload their files as well. Don't sit connected to the server while you are trying to edit your files. Do all your editing on your computer first. There had been times in the past where this was a really big problem, and hogging the server is extremely rude.
Binary mode is for transferring binary information.
Graphics, audio, video and executable programs are all examples of binary data. When you upload files through FTP, you need to decide which mode to use. Graphics and other binary files should use binary mode. There is no way to repair the files on the server, so you'll have to delete them from the server and FTP them to the server again in the correct mode. Most FTP programs have settings that let it automatically decide which mode to use, or you can set which mode based on the file's extension or by checking the data in the file.