The main aim of using LINQ to Dataset is to run strongly typed queries on Dataset.
Assume we want to combine the results from two Datasets, or we need to take a distinct value from the Dataset, then it is advisable to use LINQ.
Normally you can use the SQL queries to run on the database to populate the Dataset, but you are not capable to use SQL query on a Dataset to retrieve a certain values. To get this you require using ADO.NET functionalities. But, in case of LINQ, it gives more dignified way of querying the Dataset and giving some new features as compared to ADO.NET.