Why would you want to partially cover a pan? It seems obvious but there are different benefits to cooking with a lid or without the lid. With a fully covered pan, most of the steam released by the food is contained.
As a result, food cooked in fully covered pans take a long time to turn the brown we want, since water dripping on the surface of the stew can slow this process. Steam condensing on the lid and then returning to the food prevents liquids from evaporating and reducing. With a pan completely uncovered, on the other hand, browning can occur more quickly if the food is not submerged in liquids.
In a situation like a stew or a braise, however, we want some browning and evaporation for flavor development. That’s where the tracing paper lid option comes in: it provides a partial barrier to steam leakage without completely blocking steam from cooking.
Whenever you need to check your stew or braise you can lift the paper lid during cooking time.
If the cooking is ready, and you want a little more browning and evaporation remove the lid minutes before cooking ends. When the food is ready, just throw away the tracing paper lid.