The IELTS practice tests will help you:
Get familiar with the IELTS test format
Test yourself and get used to real test time conditions
Experience tasks similar to test tasks
Review your answers by comparing to model answers.
The computer-delivered IELTS familiarisation tests will give you a fair idea of what you can expect in the computer-delivered format of the test. However, the test format, question types, time allocated to each test part and content is the same for both computer-delivered test and the paper-based test.
You can also have a look at the IELTS preparation course to familiarise with the test format, number of questions and time taken to complete each test part.