Thoughts On Head Gear? Knee Pads? Mouth Pieces?
We'll split these into sections.
You should always wear your head gear. It protects your ears and lets you to wrestle harder. Even when you're drilling, there are moves like a high crotch to double in which using the side of your head to drive your opponent horizontally helps tremendously. This is one of the most common times wrestlers get their ears hit.
You can't be afraid to use your head when tying up or taking shots.
When your ear gets hit very hard you get cauliflower ear. Not only does it hurt, but your ear will fill up with a combination of blood and puss. If left untreated, it will harden and your ear will be forever distorted, unless you get plastic surgery. Getting your ear drained can be quite costly.
Many people outside of wrestling may not understand this distortion and will assume there's something wrong with you or think it's a disease. Some wrestlers intentionally don't get their ears drained as to wear them as badge of courage. That idea is only applicable inside of the wrestling community.
In high school, college, and many tournaments head gear is mandatory. Since you'll often be competing with it, you should practice with it. You don't want to change much when it comes to transitioning from practice to competition. If you're not used to having head gear on, then it will throw you off a little when you're forced to wear it.
Chin Cup vs Neck Strap
We recommend using a chin cup. The neck strap can sometimes choke you when your head gear gets caught on something. The chin cup also, in our opinion, looks better.
The chin cup may force you to keep your mouth closed more which in turn teaches you to control your breathing a little.
The only reason we could see for why so many wrestlers want to wear knee pads is due to style. Unless you absolutely need to wear one for medical reasons, you should go without it. They're often uncomfortable and force you to move slightly slower than you would otherwise.
The knee sliding argument is invalid. If you have good technique, your knees won't need to slide on the mat. When your knee slides, it's not always in control. You want to always be in charge of your movements. You need grip and friction with the mat so you can push off. You do not need to slide.
Try to stay off your knees, you move much faster on your feet.
If you have braces, then we absolutely recommend you wear a mouth piece. Getting hit in the face is inevitable and when it happens your braces may go through your lip which will cut you and will really hurt.
Otherwise, it's up to you.
They are supposed to make you up to 3% stronger and prevent concussions to a small degree. We're not sure how much that is true.
One benefit they don't advertise is that they help control where your teeth are in relation to your tongue. If you have the unfortunate habit of biting your tongue when wrestling, a mouth piece will certainly reduce that.
While we're on the biting topic, they will help when it comes to biting your teeth together hard. This is also inevitable. Whenever your chin gets hit hard your teeth may clash and chip.
Another benefit we see is that mouth pieces force you to control your breathing due to the obstruction in your mouth. This may make you feel less out of breath during a match.
TL;DR (Too Long, Didn't Read)
Head gear: yes, always.
Knee pads: only if you absolutely need them.
Mouth piece: unless you have braces, it's up to you.