The Data Loader is a client application from Salesforce for bulk import or export of data.
When importing data, the Data Loader loads data from CSV files or from a database connection, and the exporting of data is done using CSV files.
With the Data Loader, you can perform operations such as insert, delete, update, extract, or upsert. You can move data into or out of any Salesforce object. There is less validation when adding data.
The import wizards have fewer options and are more limited as they only support Account, Contact, Lead, Solution, and Custom object. They have built-in de-duplication logic.
Use the Data Loader when:
You need to load 50,000 or more records where the maximum is 5 million records
You need to load into an object that is not yet supported by web-based import wizards
You want to schedule regular data loads, such as nightly imports
You want to save mappings for later use
You want to export your data for backup purposes
Use web...