Mitochondria's main function is to allow molecules to enter so that they are broken down to produce ATP, energy. A mitochondria has basically four different compartments, each performing a function towards energy production. However, the principal function of mitochondria is to produce energy and control metabolism. In addition, they can act as calcium pumps, to reduce intracellular elevation of calcium levels, deleterious to the health of cells. But overall, their functions are more or less established.However, their numbers within the cell's cytoplasm can vary from organ to organ or even in a specific cell population (inter and intra-cellular heterogeneity). Also, their morphology can vary and is highly dependent on the filamentous organisation of the cytoskeleton. Nonetheless, in pathological diseases this can change, but how the mitochondria are reshaped and how they tango along with cytoskeletal filaments is a whole other discussion.
I will put two references here so that you get to learn more on it.
https://www.karger.com/Article/FullText/353883
Article Intermediate Filaments as Organizers of Cellular Space: How ...
Provided that different tissues have different energetic demands, and mitochondria are responsible for producing energy, their morphology and function can readily differ between cell types. However, they can even differ within a single cell, for instance between intermyofibrillar and subsarcolemmal mitochondria in myocytes. Our recent review may be of use to you:
Article Mitochondrial behaviour, morphology, and animal performance