I wash it in the dishwasher. It seals my pressure cooker pot perfectly and I just stick the whole thing in the fridge once it’s cooled enough. Let’s be honest, pressure cooker chili doesn’t stick around long enough to warrant putting it in a different container so with this silicone top I can put it away for the night. So far I haven’t noticed it keeping any unwanted smells but it doesn’t really come into direct contact with any food as I never fill up the cooker pot that full.
Long story short. No, you don’t really need it but it is very nice to have. I use it far more than I expected I would.