Unofficial documents for admission process
I would bet that the postgrad admission process at most universities involves at least the following steps:


You send in scanned copies of your transcripts (I am assuming here that these days most of the admissions procedure is handled electronically, in particular for international students)
Someone checks to which degrees from "well-known" institutions your degree is roughly equivalent to and convert your grades into the local scale (e.g. GPA). On this basis, a first assessment is done whether you satisfy admission criteria.
In my institution the previous two steps are handled centrally, but the next step involves academics: assuming your grades are good enough to satisfy requirements of the department (which for highly attractive departments might be higher than the regulations say), it is checked whether your profile and interests align well enough with one or more academics to be sure that a supervisor can be found, and (if applicable) whether sufficient funds are available to support you.
Only if all of this is checked positively will the university make an offer to you.
When you accept the offer, you have to supply the formal (perhaps) transcripts and have to provide evidence that these are indeed proper certificates (i have heard of cases where this has to be duly apostilled). Clearly, there is a strong expectation that your official transcripts match the ones from the first step.


Universities have a strong interest in getting students (and their tuition fees) so they want to make the first few steps as easy for the "customer" as they possibly can and "lure him in". The onerous part only comes with the last step.