Practicing with IELTS essays online might force you to focus on topics that you may not necessarily experience when you take the actual test. If your practice essays are on one particular range of topics, for example, you may become comfortable with how to transition and write about only these topics. But you may encounter a different subject range on the actual test, and thus be ill-prepared for the challenges of the test.
Many of the IELTS practice essays that you might find online may have been reproduced. These essays can be found on many different websites, and they might be widely circulated among IELTS testers. If this is the case, you may find yourself reusing ideas without authorization from practice essays. If other test takers are also doing the same thing, this can put you in a precarious position.
One practical problem that you may encounter with IELTS essays online can occur when you run into a bad essay. You may not realize it until after taking the actual test, but some essays written online are in the wrong style, tone or format. Practicing with these essays will introduce you to the wrong styles, and you might bring these with you to the test. Consult official IELTS practice guides to help you determine acceptable style, tone and format.
Practice essays are often taken in as a whole essay. You might, for example, scan the essay from top to bottom, and attempt to make general observations about the piece. This, however, can be an ineffective practice, as it is best to learn the essay format in parts. The introduction, body and conclusion paragraphs should be learned separately, and once these parts are learned, they should then be put together as a whole.