What's major difference between export and backup and when to use backup and when i must use export? When I was working with backup,I found export and backup have ability to save your current data.But there must be some difference between them.
Both are for to backup the content in sharePoint,however the backup done through content db will restore the exact instance you have taken backup of whereas the export will create a new instance of the content. Means from export the siteID,ListID all changes and backup through content db the id's remains the same
Backup-SPSite is generally used when you want to replicate the entire site collection (including all subsites) to an existing web application.
Export-SPWeb is generally used when you want to replicate just a single subsite to an existing site collection.
Also below links are worth to read for other major differences: