Usually, no. You should keep your goods with you and be ready to show them to Customs before dropping off your bags.
If you need to show your boarding pass first, you can check in, but don't drop off your luggage until after Customs has seen your goods.
In some countries, you must check in first. In that case, ask the airline staff to put a tag on your luggage and give it back to you.
After Customs checks your goods and stamps your Planet Tax Free form, they will send your luggage to the airplane.