Freediving & Spearfishing Floats are very important! They make sure that your dive buddy is always able to locate you, and even more important: boats know that there are people in and underwater. This can be life-saving.
Floats mainly come in two different versions: hard floats and inflatable floats. Both obviously have advantages and disadvantages, depending on your dive spot. Hard floats are the preferred choice for shore entries, due to their durability and abrasion resistance against rocks. Yet, they are heavier and can be more expensive than inflatable floats of a similar size. The main advantage of the inflatables is definitely their light weight at any size, which makes them easy to carry and tow.
You can also attach your speargun to your dive float, by connecting it via a float line. This way, you will be able to let your gun go when you shoot a fish and still be able retrieve it at any time. You can come up to breathe, make sure everything is in order and go back for your gear easily and safe.