In asexual reproduction a single parent produces offspring on its own. No gametes are made and there is no fertilisation, so every offspring is genetically identical to the parent and to its brothers and sisters. They are clones. Bacteria dividing and strawberry plants sending out runners are examples.
There are clear advantages. The organism does not need to find a mate, which saves time and energy and works even when individuals live far apart. The reproductive cycle is rapid, so a population can grow quickly when conditions are good. For example, a bacterium that divides every 20 minutes doubles three times in an hour and makes 8 cells.
The disadvantage is that there is no variation in the population. All the individuals are clones, so they all share the same weaknesses. If the environment changes, or a new disease arrives, every individual is equally vulnerable and the disease could wipe out the whole population.