XTR Derailleur Cover with Tongue necessary?

[HaakonJohansen]

Does anyone know if this part is necessary? A bit stupid of me, but I took it off, and now I can't find it, so I just wonder if I need to order one or if it's a part that bike shops typically stores, or if I can do without it. It's part number 20 in the picture below, so you guys can see where it's actually used.

[CGT]

No way the one is necessary.