Most of us are already using buffers, even if they're not labelled as such. Whether a dedicated buffer is needed almost requires looking at each cable and component in the signal chain. I look at each device's output impedance, and then the input impedance of what it's going into. You typically want low Z going into high Z, but how much that even matters depends somewhat on the length of cable between the two.
Unless a pedal/device is true bypass, it's acting as a buffer. Your dedicated buffer pedal is only helping up to the point of the next buffered device in your chain, but sometimes that's all you need.
One of the most important places for a buffer is coming right out of the guitar, before going over a cable to your pedals or amp. No matter what other devices you have in the chain, they almost certainly have a better output impedance than your passive pickups. That's part of why I'm a huge proponent for digital wireless (or active pickups, if that's your thing). Some people don't like the sound of digital wireless, but what they're hearing is what their guitar really sounds like without the load and loss induced by passive pickups over their instrument cable.
