the most straightforward example off the top of my head would be that hair follicles have no conceivable reason to react to testosterone. removing DHT receptors from them would have no adverse effect whatsoever.
We can also live just fine without an appendix. Literally the only thing the organ can do is suddenly develop a severe infection and kill you without surgery which has only become reliably available in the past 100 years or so. (Blah blah bacterial reservoir or whatever: that's of evidently very low value compared to sudden and painful death)
There's also no reason we shouldn't be immune to funnel web poison: cats make an enzyme which deactivates it, whereas primates don't.
have you read the story of dr. adrian thompson's ai generated fpga ? the story goes that removing seemingly redundant components caused the circuit to fail because of second order effects. for that reason, i try to avoid sweeping statements like 'no effect whatsoever' when it comes to playing god