Does looking at the fretboard while playing reduce your speed ?
Is it better to practice without looking at the fretboard ?
I would only suggest looking when you dont know the song your playing.
Then once you know it, play it without looking, thus increasing your skills to play songs without looking, and you gradually learn where to put your fingers on the fretboard without needing to look.

Some people tend to practice infront of a mirrior, sounds strange but it actually really relax's your shoulders and other stuff. I found this out from my guitar teacher, and i found that it does work, although i dont use it as the only mirror that i have which would allow me to play a guitar infront of it would be the bathroom, so im sorta screwed if somebody needs to pee.
Fender Special Edition Custom Telecaster FMT HH in Crimson Red
Reverend Sensei HB FM in Tobacco Burst
Fender Vintage C Neck, HH, Surf Green Nitrocellulose (Handmade)

Egnater Rebel-30 MKI Head
Egnater Tourmaster Series 412B 280W 4x12 Cabinet
if you dont look at your fretboard when you practise you're probs not gonna know what the fk your doing
Quote by SEALSniper1152

If you take a jar, and whisper what you want to hate into it, then close the jar, coat it in crunchy peanut butter, and shove it up your ass. I'm pretty sure you could hate everything after that.
No, you should be looking at the fretboard while you play, as much for acuracy as anything. It wont slow you down. Its only when you come to a point when you know it so well (the song you are playing, or the entire fretboard) that you dont need to look. All to do with muscle memory...
I look at the fretboard when I need to and when I don't need to I don't. I know when I don't need to look at the fretboard when I find myself playing not looking at the fretboard.

I think that makes sense. Basically I mean I don't make a conscious decision to look or not too look, I just find myself looking when I need to then naturally and unconsciously I'll start to not look, if you follow me
Look at it when you're unsure if you're hitting all the right chords/notes. In time you will gradually learn from instinct exactly where to place your fingers so you'll stop looking as much/at all.