1. Keeps the tail end of the Mavic higher off the ground so that if you take off from grass, it wont stain your blades
2. Same as above if taking of from a gravel surface, rocks wont chip your props.
3. Most important, the leg extenders protect the front landing legs from getting broken. Very common to many Mavic flyers on a hard landing.
1. Can interfere with sensors
2. For most hard and soft cases, you have to take the extenders off every time you put it away.
For less than $2 (ordering from China) you can get the soft silicone leg extenders. That's all you really need. They provide a little bit of extra clearance and some shock resistance and weigh almost nothing. They also won't scratch up the legs when taking them on or off, and they store anywhere.