hi,
a confirmation letter is absolutely and most importantly plays a crucial role in the notice period after resignation.
some companies have a process of keeping new joiners on probation for three to six months. Based on the level of their performance are they confirmed by getting a confirmation letter
The confirmation process is done in consultation with their reporting boss-if the employee's performance was as per the expected standards.
the main difference on people with probation and those who are confirmed is that people on probation, after resignation have to serve lesser notice period than the ones who have been confirmed. The logic behind that is that the person not confirmed is not suitable for the company and can be asked to go in the mimnum time frame. Alternatively, the person who has been confirmed means that he must have been a good worker, therefore, since it takes time to replinish a good resource, he needs to serve a longer duration of notice period.
I believe its a very important process and must be followed wherever quality performance is top priority.
Hope this helps you!
regards