Candidates can know IELTS content well and still lose time because they are unfamiliar with on-screen reading, typing answers, moving between questions and managing a visible timer. Repeated computer practice makes those actions routine.
Full mocks are best for pacing and stamina. Section practice is better when one skill is holding your score down. The fastest improvement loop is mock, diagnose, drill, then mock again.
Do not stop at a band estimate. Review which question types caused errors, whether time ran out, whether answers were changed late, and which skill repeatedly falls below your target.