I absolutely need a line on the ball for putting. I've just started using a check go but used a cheap ebay ball liner before that. I haven't used the "square the club" line for putting or driving - I'll have to add that and give it a go.
If you are trying using a line for the first time, you have to put in a couple of practice sessions on the practice green to experiment with where the ball is in relation to your body when first lining up the ball. I'm right eye dominant so when I squat down to aim the ball, my right arm is just inside my right knee. Then you back up several feet to confirm the line, align your putter to the line on the ball and putt. When you stand over the ball, the line will not look like it is aimed where you want, you have to trust what you did. When I am standing over the ball, all I am thinking about is pace since I already figured out the line. It's improved both my accuracy starting on the intended line and my pace control. YMMV.
But I am definitely in the minority in my senior club - most people do not have a line on their ball although judging from their lack of ability to start the ball on a good line, some should try it.