What is crital information and non crital information

Critical Data is kind of a grey area.
From an IT point of view it is Databases (sql, oracle, exchange, lotus
notes, etc.) And most servers (Domain Controllers, DNS, DHCP,
Certificate Authorities).  What isn't critical data are the end users
pictures of their kids that they took with their new digital camera or
other personal files like that. Unless its the CEO, President of the
company, Big Wig, Head Honcho, etc.

It depends how you look at it. Some information has to be backed up
and held for a set period of time to meet various Federal or
State/Provincial guide lines and Laws. In that example it would
certainly be deemed critical. Some people don't view phone lists,
company directories, and quarterly reports and such as critical data
which for the most case the loss of one or two such things it would be
trivial. But to lose a large number of such items and in large
corporations the man-hours to recreate such items can turn in to a
large sum of money and not including the lost productivity of having
to recreating such documents. Backing up data in the long run is much
more cost effective than the time spent recreating information