Tissue culture is a method/process of propagating plants that are clonal or identical to the parent. In some ways it is a brutal chemical process, and therefore the plants are not actually always identical because of the damage/mutation that happens to the DNA. Some species suffer more variability than others, such as Bananas. Some chimeras, in Bananas will not come true when tissue cultures. It is often used to produce many plants from a small small amount of genetic material - sort of like turning one cutting into 100 cuttings, so that you can produce more plants in a shorter time frame.
With bananas, for example, it can be done on your kitchen table for fairly minimal cost and equipment, and without a lot of specialized knowledge, if you follow simple procedures and maintain cleanliness.