There are more cons than pros, honestly. It's possibly more accessible than other methods in terms of materials required because there are sharp objects everywhere, and I guess people romanticise the idea, but it sucks in almost every other way.
1) It really hurts, especially if you're not used to cutting.
2) The consequences are fucking dire if you end up surviving. Depending on where you cut, you might lose function in a limb or a hand or whatever. You'll also have a lot of scars. My attempt was impulsive and I didn't even get that far before I got caught, but I still have some very visible scars on my wrist.
3) You need to know where exactly to cut. The blood from normal wounds will clot after a bit, meaning you have to apply a blood thinner or regularly put water on them to keep them bleeding. Arteries will bleed a lot, but they're really deep in there and hard to get unless you're lucky.
4) It's much easier to chicken out of it than other methods (imho). Methods like, say, jumping or using firearms have one trigger that sets your death in motion. That's starting to fall and pulling the trigger respectively. At that point, there's no going back. You psych yourself up to do that one thing and then you might as well be dead. With cutting, you have to do it over and over and over and over again and experience great pain every time.
5) It's statistically unlikely that you'll succeed (from what I've heard).