There are several alternatives when entering data in iDempiere.  You can do it manually via the window itself.  Another way to encode data is through the available import facilities (i.e. CSV or import windows). Still another way is through ETL (Extract, Transform and Load) software such as Talend ETCL.  Each one can be used as needed. You will get the same result i.e. master or transaction data loaded in your window.

Manually entering data is advantageous since you get your data loaded as soon as you save it.  You also don’t need to spend time preparing your data for import. The disadvantage is you need to type each record manually each time. Importing via CSVs, the iDempiere import facilities, or ETLs skip the manual entry of data. You spend time preparing the data but it is faster specially if you are dealing with thousands of records.

We’ve used all different data entry options to import and/or update data.  It does take time to set-up the import files.  Sometimes, it will take several iterations to perfect the import files.  Once you are able to import though (using CSV etc), you will have a template to use for future imports.   

Talend ETL allows you to transfer data from several different sources such as excel, web Services and other database instances.  We love using Talend and have used this extensively when transferring data from other data sources such Excel, MySQL, CSV files etc.  

There are many ways to enter your data in iDempiere.  In my experience, either one will be a great way to enter data. It is always up to the user or the technical need to determine which to use.