A pore in a microstructure, unless desired, is a disadvantage for the properties. In fact, in nearly all of the materials, a pore will be the starting point for the rupture of the material. It is the initiation point for the cracks. Furthermore, a pore is usually quite hard to get rid of. Those techniques described later involve a high temperature process. However, even those processes can sometimes make the pore even bigger. Pores with large coordination number (surrounded by many particles) tend to grow during the thermal process. This is caused by the thermal energy being converted to a driving force for the growth of the particles which will induce the growth of the pore as the high coordination number prohibits the growth towards the pore.
For many materials, it can be seen from their phase diagram that multiple phases can exist at the same time. Those different phases might exhibit different crystal structure, thus exhibiting different mechanical properties. Furthermore, these different phases also exhibit a different microstructure (grain size, orientation). This can also improve some mechanical properties as crack deflection can occur, thus pushing the ultimate breakdown further as it creates a more tortuous crack path in the coarser microstructure.