First timer.

Bungees are not essential as long as you are using a stretchy spearline e.g. nylon monofilament but they provide 3 benefits:

1. I makes it easier to reset the spear-line when re-loading.

2. It absorbs excess energy at the end of a missed shot, helping to protect the spearline & thus helps prevent spear loss.

3. It helps avoid rip-out when you spear a fish without killing it outright by absorbing some of the shocks that fish sometimes make in order to escape (I'm picturing a mullet as I type this ).

Muzzle bungees do add a little mass & hydro-dynamic drag at the muzzle. Some bungees are much lighter/heavier/bulky than others. Some include metal clips and/or swivels of various sizes/strengths.

Some bungees include a metal clip or you could use an easy to untie knot (e.g. sheet bend/ double sheet bend) to connect the bungee & spearline. This gives you the option of pulling the entire spearline through the fish if there is a problem forcing the spear back through the way it came.