How important to have a Signal Blocking case/holder                                     

Signal-blocking case are designed to help insulate you from a very particular brand of electronic
pickpocketing, called RFID/Signal skimming, by hacker. The concern is that car keys now come with embedded radio frequency identification chips. When activated by an RFID reader, these chips transmit certain types of information wirelessly, so that you can open your car door and start card engine.  The downside: Anyone with an special RFID reader can activate those chips and pick up whatever information they're designed to transmit. And, if they're sneaky about it, they can do it without your knowledge.
Hackers have made headlines over the years by demonstrating how a handheld RFID reader can "skim" sensitive information from people's car key at a distance of several feet. They can open the car and steal it without your car key.
Car key signal blocker case making them harder to read remotely. 

How the hacker steal car from scanning the wireless car key

Video: https://synteksmart.en.made-in-china.com