If you have a large house, there's no use picking a robotic vacuum that won't work for a long duration. If you end up picking a robotic vacuum that can only clean half your house and then return to recharge, it might be more of a hazard than a help.
Most robotic vacuum cleaner work for an hour or so before they need another charge. If your home is bigger and would take more than an hour to clean, you might opt for a model that has a larger battery life and a shorter charging time. Otherwise, cleaning your house can take the whole day and be a hindrance to everyone living in it.
Also, not all vacuums are suitable for all floor types, especially thick carpets. If you have any thick shaggy or high-pile rugs around your home, you may have to still clean them with a hand vacuum.