Well not to play Dr. Obvious, but to quote a spec people claim to be
following:
If a BGP speaker detects an error, it shuts down the connection
and changes its state to Idle. Getting out of the Idle state
requires generation of the Start event. If such an event is
generated automatically, then persistent BGP errors may result
in persistent flapping of the speaker. To avoid such a
condition it is recommended that Start events should not be
generated immediately for a peer that was previously
transitioned to Idle due to an error. For a peer that was
previously transitioned to Idle due to an error, the time
between consecutive generation of Start events, if such events
are generated automatically, shall exponentially increase. The
value of the initial timer shall be 60 seconds. The time shall
be doubled for each consecutive retry.
So if you want to see it used, get on your vendor about it...
Also, RFC1771 is pretty out of date, the "least incorrect" reference
currently available is:
http://www.ietf.org/internet-drafts/draft-ietf-idr-bgp4-12.txt