Vacuoles are used to contain harmful materials, waste products, and small molecules. They also maintain pressure and an acidic pH within the cell. While most, if not all of plant cells have at least one vacuole, not all animal cells have one. In animal cells which contain vacuoles, they aid the processes of exocytosis and endocytosis among others and play a critical role in a process known as autophagy.
Autophagy, ('self-eating) is a catabolic process in which cell parts that are no longer functioning correctly or are simply no longer necessary are broken down. This occurs by first isolating the targeted components / organelles and then fusing lysosomes to them. Lysosomes are organelles that contain acid hydrolase enzymes. This process is especially beneficial during periods of starvation in which the cell may digest its own components for survival.