Having a visa on arrival applied for can take you from one to two hours to several hours to be able to apply for one and get it under your name. This means that all this time you will have to spend inside an airport itself. While when you apply for an Emirates 3 days visa through an online method you can get this visa delivered to you while you are still at home or when you are still working in your office and hence applying for an Emirates visa through an online method is much more convenient.