A cantilever design-form adds more flexibility[1] in (piezoelectric) energy and power harvesting:

1) A DC (pseudo-static[4]) part of the flexibility is a helpful architectural design because, we are able to separate[2,1] the (space and/or the) sites of the (PZT) source and the load.

2) An AC (dynamic[3], additional) flexibility because, we are able to modify the linking[1,2,3] of the power harvesting, and specific demands (and properties), among the (PZT) source and the load.

1. Piezoelectric energy harvesting https://specialtyfabricsreview.com/2017/04/01/piezoelectric-energy-harvesting/

2. This ("same") flexibility factor is considered as a major engineering breakthrough (factor) in architectural designs.

a) Contemporary Cantilever House Design by Paris Architects https://www.trendir.com/contemporary-cantilever-house-design-by-paris-architects/

b) https://en.wikipedia.org/wiki/File:Cantilever_bridge_human_model.jpg

c) https://www.britannica.com/technology/cantilever

3. https://en.wikipedia.org/wiki/Euler%E2%80%93Bernoulli_beam_theory

4. Actually, it is the (main) steady state mode of the self-excited oscillator. a) http://www.mouser.com/ds/2/40/piezo-43596.pdf ; b)Conference Paper Self-excited Piezoelectric Cantilever Oscillators

A cantilever is a rigid structural element in the form of plate to support from which it protrudes. Piezoelectric with cantilever is an application of the piezoelectric materials in infrastructure monitoring, with advantages of flexibility and easy encapsulation, such as in pavement blocks and bridges.

Dear Tae,

Your question is not clear for me. If you want to know why cantilever beams are used to harvest energy from piezoelectric materials the reason is most of the time specially for vibration energy harvesting having the higher strain can be resulted in higher power efficiency. Actually you need to know about your source of vibration or pressure you like to use also know about d31 and d33 modes in piezo materials. If you like to use just pressure the type of piezo material should be chosen carefully and also cantilever beam is not necessary to use. It is completely depends on your design. Good luck

If you compress a piezopolymer you can get about 5 volts out, but if you bend it you can get almost 100 volts. So, they like to use the cantilever instead of the compression, because it's easier to get higher voltages.