If you need girth high erection 50-80% is needed. And if you want length then go on low 20-50% erections. The jelq works on the tunica by adding more and more pressure to it. Every time when adding the pressure it expands more and more. So when you get erections more blood can come in and make a bigger and harder dick. It’s good because it can work on bout girth and length. But most people do it for girth, that’s what I read.
Don’t squeeze you’re dick till it dies, you need to get some pressure in it to do the work out. But don’t over do it. Don’t you know what every good PE-er says: “some times it’s better to do less the more” understand, don’t overdo!