No one has become an expert on the first day. You need a lot of practice to master any subject. Only Practice makes a man perfect.
Online practice tests can help you in many ways.
1. Flexible test schedule
Do not worry about the practice questions/paper for Class XII. If you have a computer or smartphone with internet, then you are all set for the practice tests! You can give your test from anywhere and anytime. This saves your time and allows you to take many practice tests before you attempt the main exam.
2. Instant result and feedback
In a pen/paper test, you need to wait for the test results to analyse how well you did. In an online test, it gives instant results and feedback which is very useful. Depending on your results, you can figure out how to go about with the preparation and also saves lots of time.