Subject: What is the purpose of chromosome walking?

As far as my understanding, chromosome walking is performed by taking a 
clone of known sequence, that we know lies near some region of interest, to 
probe genomic library generates by different restriction enzyme. 
In this way, we will get two clones that will hybridize with the probe. 
Both of them have overlapping sequence with the first probe. Then, one of 
them is used to probe the genomic library where the first probe is derived 
from. Similarly, two clones shows hybridization (one is the 1st clone used 
and the other will be new overlapping clone). Then, the newly overlapping 
clone is used as probe for the 2nd library again. This is repeated 
gradually building up a partial restriction map, until we reach the 
particular locus of interest. 

But, what's all this about? To sequence the locus of interest? or just to 
identify the surrounding sequence of a particular known gene? Is there any 
obvious pratical example for this? thank you.

Re: What is the purpose of chromosome walking?