According to many compliance guide line saving the signed logs are highly recommended for at least 2 years. The importance of logs has being recognized by IT security area people. If you have recognized suspicious access, symptoms or errors on your system(in any other reasons) you can download the signed logs to analyze with following instructions.
1. Settings > Data Management > Signed Logs
2. In following windows, select the specific year, month and date of logs that you want to download.
3. Here are many type of Archived Log files. Log files are compressed by bzip2 which often found on Unix-based systems. If you are a windows user you can follow this link to download a decompressor. Basically, the collected.raw.bz2 file includes typical logs you might want.
Please follow this link to see the brief file description.