Dear Archana,
I have not used this tool in my career. However, this tool can be used in counselling, interviews, "presentation skills" training program, etc.
For example, in Johari Window, there is "unknown self", this means some information is known to others which you do not know.
Certain mannerisms, styles and rhythm of an individual while interacting with his colleagues, peers and subordinates may not be conducive. The individual may not be aware of this. You can point out the same and correct himself (he becomes concsious only when he is told about it).
Similarly, the "Open self" is known to both the individual and the perceiver. This trait can help his boss to identify his strenghts and weaknesses.
Other two ("Known self" - which the individual only know, "dark self" individual and perceiver both have no idea) will not have much to offer. Unless the individual volunteers himself to disclose some facts or secrets about himself, helping him will not be possible. We can encounter this type of trait, during interview.
V. Balaji