Fly sheets

Fly sheets are good from a bit of insulation from cold and heat.

If the roof is water proof and you are in a hurry why not leave em off.

HI - what you are referring to are called BED FLYS. They are available in different ways. Plain flat "sheet" which slides in a sail track when you set up and is removed when you pack up. They are also available permanently fitted to the roof in the sail track. They are housed in a zip up bag which is simply screwed to the sail track in 2 or 3 places. Now the bed fly can also have sides on 1, 2 or 3 sides. The modern versions have a mesh screen side on all 3 sides which provides ventilation and also privacy during (mainly in the day)

you do not need to use them uness you choose to. Some reasons to use them include protection from rain, dew etc which may cause the roof section to become dirty on outside and even mouldy on inside if you dont keep it aired. It also become an insulation from the weather for your comfort. The bed flys will also protect your beds when you setup and pack up in wet weather (will need practice to get this down to a fine art)

One easy way to pack up the zip up bag flys with 3 sides is to drag it towards the opposite end and lay it on your van roof. then with a person each side begin to fold it up by taking it back towards the bag.

If you are just doing 1 night stop overs, you could get away without them but i guess over time you will see a deterioration of the canvas roof on the beds. With practice you will get them up and down pretty quickly. cheers....