I don’t think they are rubbish, but if you are good at following plans, then a real one will be much more effective. It probably also depends on your fitness level. The more serious of a runner you are the less effective it’ll be. For beginners it probably doesn’t matter as much and any kind of running will yield results.

Personally I am not structured enough to follow a plan, so sadly my training is probably inefficient in general. The way I use them is that I look at the daily suggestion before I start my run, and if it looks like something I am in the mood for, then I’ll do the workout. Otherwise I just ignore them.