Acoustic guitar adjustable saddle

1. What is an adjustable saddle guitar?
2. When should I replace my acoustic guitar saddle?
3. Why do acoustic guitars have no adjustable bridges?

What is an adjustable saddle guitar?

If the strings are too high or too low, you have to adjust the action. To adjust the action, you need to raise or lower a part of the bridge known as the saddles (the parts just in front of the bridge where the strings sit). You raise or lower the saddle by turning the hex screws with a tine hex wrench.

When should I replace my acoustic guitar saddle?

Never, unless they wear so low that it affects set up/function. I own/have owned probably over 30-40 guitars over the decades. Never kept a spare saddle around or had to replace one because of wear. Have replaced them in regards to a guitars action.

Why do acoustic guitars have no adjustable bridges?

Two things from a physics perspective that would argue against adjustable bridges/saddles on acoustics. One is the transfer of vibration to the sound board. Having that additional apparatus between the string and sound board would likely result in some tone/volume loss.