The enclosure just protects the prints from drafts, which can cause sharp corners to curl. The most common instance of curling I had was printing square shaped PETG parts that needed to be flat on the bottom. I got away with no enclosure for years by setting up my prints with tall, thick skirts close to the part (draft shield), and a thicker brim. I was basically tacking down the corners with extra plastic to keep them from curling up. However, PETG was just a bit too curly for this print.

The few times I absolutely needed draft protection, I used a trash bag. After I needed to do several batch prints for a cash job, I decided a $30 enclosure would be much more practical.

So far, my Ender 3 has met my needs very well. Any upgrade would be a “want” at this point.