Why and when a breach of contract claims are requested?

Contract creates an obligation on the parties to perform their agreed thing within the ambit of rules and regulations of laws applicable.

Why is ---? It creates a loss(may be any manner) to the party of the contract who is willing to perform his/her part and expecting the other party to perform his/her part as it is obligation on the party, if otherwise(breach of contract i.e failure to perform the contract). 

When ---? If there is a breach in performance of the contract by one of the party within all the parameters agreed by the parties, the other party can proceed by filing a suit of specific performance of the agreement and/or for claim of damages. 

My 2 cents. Thanks.

Construction wise :

Special requests by the end user

Changing in the specs of the project

Changing in the study of the project

Changing in the design of the project

Payment delay

Ok, the shortest possible way to explain it:

1. There is a Contractual Obligation

2. The Contractual Obligation has been breached by one party

3. This breach of obligation has caused damage to another party

4. The party which suffered damage can request breach of contract claim (provided he has timely notified and has substance to prove the damage)