Can Informatica be used as a Cleansing Tool? If Yes, give example of

Yes, we can use Informatica for cleansing data. some time we use stages to cleansing the data. It depends upon performance again else we can use expression to cleasing data.
For example an feild X have some values and other with Null values and assigned to target feild where target feild is notnull column, inside an expression we can assign space or some constant value to avoid session failure.
The input data is in one format and target is in another format, we can change the format in expression. we can assign some default values to the target to represent complete set of data in the target.