The MVV is a special entrance visa which is needed by a non EU/EEA resident to enter the Netherlands. It is valid for 90 days and will only be issued in combination with a residence permit.
Once your application for an MVV and residence permit is approved, the IND (Dutch Immigration Authority) will inform the Dutch embassy or consulate in your home country. You will then have to arrange an appointment with the Dutch embassy or consulate general to have your passport stamped with the MVV visa and also to provide your biometric information (fingerprints, passport photo and signature) in order for the IND to make your residence permit.
The 90 days cap is to allow time for you to make an appointment at the Dutch embassy (which normally can take more than 2 weeks) and prepare for your departure to the Netherlands. You have to travel to the Netherlands within the 90 days. Once you arrive in the Netherlands, you will have to wait for an additional 2 weeks before your residence permit can be collected. It is important that you ensure your MVV has not expired before you receive your residence permit.
Take note that you cannot request for an extension of the 90 days. If your MVV visa has expired (the 90 days is over), your sponsor will have to submit for a new application and you will have to pay for this new application.