As you are probably aware crystals all have an energy and the shape of a crystal can affect their energy. A crystal being in a certain shape does not make it more powerful, it just changes the way you experience the energy. Let’s look into why they are different shapes and the benefits of the different shapes:
Tumbled
This is probably the most common way you will find crystals. They are great as they are pocket size! As they are tumbled the energy is balanced all over and not going in just once direction. The practical size also makes them practical for magick and spells. Multiple can also be worked with at once as of their small size. For example they can be split up and placed on each chakra during a meditation.
Raw
Raw crystals are in their pure form, completely untouched from Mother Earth. They are not tumbled and are just how they would be before they were moved from where they grew. As they have not be reshaped at all means they have irregular energy. This is why some people feel they are more powerful but this is not the case they just feel more connected with them in their natural state.
Clusters
Clusters are beautiful and have super special energy. Their energy is very strong vibrationally. The different points on the cluster send energy in all directions. These are great as the energy will reach all parts of the room it’s placed in. 
Pyramid
Pyramids are great for manifestation. This is because they anchor the intentions through the base and then they are strengthened through the point. Write your intention or something you would like to achieve on a piece of paper and place it underneath the pyramid. 
Sphere
Spheres are special as they have even and balanced energy. As a result of this they are very calming, this makes them good for meditation. They radiate their energy in all directions and also make a great centrepiece!
Point
Points direct their energy as you can guess, through the point. This amplifies the energy, making them great for setting intentions. Points also raise the vibrations so are a great addition to your collection. 
I hope you have enjoyed learning about why crystals are different shapes and have learnt something new!