backports vs testing (etch)

[Martin Paraskevov]

I am confused as to why backports.org exists. If I want to use the latest software,
should I use backports.org or I should upgrade to etch (I am currently using sarge).
What happens if I use backports for some time and then decide to upgrade to etch.
Will I end up with a broken system? What is the philosophy of backports?

Thanks,
Martin