It is just like TOEFL, GRE or GMAT.
It measures things such as how to dress for a semi-formal dinner party for business, or the awareness of how to talk to people from different cultures with sensitivity.
There are probably 10 other people who want the same job you do. The one thing that your employer will value most is how well you work with others. But guess what? All the same 10 people will say they work well with others! So how can you stand out? Getting IITTI-certified gives you that edge.