Welcome to the bane of all spearo's, the FLOATLINE!!!!!!
Ok, the float is attached to either 30 or 40m of floatline. This is attached to the gun or shooting line in this instance. There is normally wind or current around, so your floatline will most of the time be fairly straight. Spearo's tangling with their floatlines are a common occurence, but you soon get the knack of diving with one. Floatlines are a topic completely on their own. Some guys make their own with PVC tubing, so that it floats and tangles less.
The benifits of using your gun as a break-away rig is that should you shoot a big fish, you can only lose your spear and floatline and not your gun. ALso when hunting fish like GT's, that love to swim through caves and reefs when shot, there is no damage to your gun. The most important reason for me is that i like to have a gun in my hand. Some-times it gets a bit hairy with sharks trying to steal your fish and you being un-armed. Even a unloaded speargun is a great physcological comfort, well for me at least.
When shooting smaller fish, a reelgun is my choice. No floatline. Simply a reel attached to the barrel of the gun. In this way, i've always got the gun in my hand. When diving like this, your greatest fear is other BOATS. Since you have no float, they can't see you. MUCH MORE DANGEROUS THAN ANY SHARK!!!!!!
Hope this helps.