Weeds left unattended to in a garden can take over other plants and look unsightly. They also take water and nutrients away from your lawn and other plants and can also survive in tough, dry conditions and reproduce quickly.
The best way to remove weeds is to tackle them while they are young before they flower and set seed, creating future generations of weeds to contend with. Generally hand pulling of weeds in garden beds or use of a non-selective herbicide will take care of your problem in hard to access areas like garden paths.