If you want to backup the entire system, it is best to do it cold by booting into something like clonezilla. Then you image the whole drive as a snapshot. You can later restore by booting into clonezilla again or similar and copying the disk image back over the disk.
If you want to backup a database, such as postgres as you mention, you should use database tools particular to your setup. For example, I use AutoMySQLBackup to backup my MySQL database with rolling backups. I put the command in a crontab that checks if my USB drive is connected and, if so, runs the backup.
Thirdly, if it's your personal machine, you should also be backing up /home. For this, I use "Back in Time" which keeps track of changes in files. This protects you even from problems like overwriting or deleting a file by mistake, undoing edits and other user errors. Lifehacker has a good overview of it. It's also a good idea to occasionally make a full copy of your /home to a USB drive and store it off-site such as at your office. You can use an encrypted USB drive if that's a concern.
Many people find the full disk clone/restore isn't really less hassle than just doing a fresh install. Many people also don't have their own SQL databases. That's why you see the focus on just /home.