As you get better in spearfishing you'll move up from a three prong pole spear to a speargun. Proper maintenance on your speargun will result in keeping your gun shooting strong and accurate. One thing to always maintain is your monofilament line or shooting line on your gun.
Having new mono on your gun allows your gun to shoot more smoothly with less friction or chances of getting caught on your trigger release or reel line anchor guide. Through many dives your mono will begin to have creases from normal wear and tear and from wrapping your line around the trigger release and speargun grooves. Also, if your line gets tangled on the reef it could begin to fray or cause more heavier creases which overall weakens your shooting line and increases your chances of losing fish.
& then theres times you shoot a large fish that takes you for a ride, meanwhile your mono is wrapped around practically everything including yourself. This is when spearfishing can come very scary. My best advice for you in any sticky situation with mono is just to not think about it and cut the line. Even if you don't have a backup gun for the day or extra mono to re-rig your gear. Just cut the line, land your fish and call it a day. This is given that you have a dive knife on you, which ever diver should have a dive knife as a basic survival equipment.
Here's a quick video I did rigging new monofilament line on my KAP Spearguns 100 after cutting my line to land a 16.5 lb Omilu.
Changing your mono is relatively fast and easy. If you don't have your own rig gear to change it yourself you can visit your local dive shop and i'm sure they will rig it for you. Or you can invest a little money now to save money later by rigging your own gear.
Monofilament 200lb: https://amzn.to/2yRpqLE
I normally use Hi-Seas Grand Slam mono and they have this conversion chart thats helpful for choosing your crimps. Or you can check out Neptonics where you can order Mono & Crimps together so you don't have to worry about ordering the wrong size crimps.