Our standard Buffer (not Buffer+) is just a single input buffer. There is no buffer at the loop in. The loop in and amp out jacks are simply there for convenience of pedal board routing, and set up and tear down. It basically makes the buffer the central routing point of your pedal board.

In the Buffer+, we have a buffer at the loop input because it's essential to the extra functions of the Buffer+, such as the noise filter and output boost. Alternatively, you can also use the Buffer+ as a buffer for your effects in front of the amp, and as an fx loop buffer by sending the fx send from your amp to the loop in.

In other words:

Our Buffer has a buffer between the guitar input and loop out / tuner out

Our Buffer+ has a buffer between the guitar input and loop out / tuner out, and another buffering stage between the loop in and amp out

No, you don't. If nothing is plugged into the loop in, it is automatically connected to the loop out.

Yes, the buffer works great in an fx loop! Although to get the most out of it, you'd want to have the buffer as close to the amp as possible so that the cable run to your amp's fx return is very short. If you need a buffer going into your amp as well as at the pedalboard input, you're better off buying the Buffer+.