Computer based examination has multiple benefits such as:
The candidate can review or re-answer any question at any point of time which was not possible in the offline mode. This removes the problem of bubbling error
The candidate can also mark a question for review to later come back and solve it.
The color schemes properly differentiate between questions answered, left unanswered and marked for review.
The test requires the candidate to be comfortable with the mouse and this is relatively easy keeping in sight the benefits.