i am not sure what hole you see on the chissis but if that hole leads to the outside of the car, you DEFINITELY want to connect it.
As the engine run, it charges the battery. When battery is being charged, it creates hydrogen gas. The purpose of the hose is to let the hydrogen gas escape from the car. If the hose is not connected, the gas will built-up around the area. A good dose of hydrogen gas plus a spark, a light from someone smoking maybe, may prove to be too james bond for you. Don't forget your battery is under the rear seat.
Likeihood is not that high but its a risk we all want to mitigate. I myself lost that hose but my battery is in the boot. just find the right hole and plug it in!