It is likely that a conviction or a medical condition would impact your chances of being granted a visa. However, the tricky part is that when you apply for a short term temporary visa applications, you are not required to provide police certificates or medical certificates.
More than often people ‘forget’ to mention convictions or medical conditions on their application or to their adviser. They do not know the implication of their action.
Immigration NZ keeps all the application forms electronically. When you apply for a further visa, immigration officer checks the previous file based on your client no, DOB and full name. It means that any subsequent visa application you make will be checked against previous ones that you submitted.
For example, when you apply for a visitor visa, you didn't include your de facto partner but it will affect when you apply for a residence visa and try to include your partner in the application.
Another example would be if you drove under the influence in your home country and didn't declare when you apply for a visitor visa. Then when you apply for a residence visa, you must provide a police certificate. In this case, Immigration NZ found out that you didn't declare the driving under the influence and you will be questioned whether you are trustworthy and your application is bona fide.
Therefore, if you provide any false, misleading or omitting information that could be used as a ground for declining your visa. In most of the cases, it is best to consult with a suitably qualified and competent immigration adviser to have a peace of mind.