Whether you should train to failure is heavily debated. Training to failure on multiple sets, each and every workout though is generally not a good idea, IMO.
Let's take your example: what you'd wind up with is total burnout on your first set, which you've pegged at 12 reps. So, you spend all your energy (or a large portion of it) ripping through that first set. Well . . . if you want 10 reps in your next set, you may get it if you rest long enough, or you may have to reduce the weight some. And you'll have to do that on every set. The result? Your working w/ weights that aren't very close to your one-rep max. That's not a very good way to build strength, which means you will have a tougher time adding weight to the bar. And that plays a BIG role in how much you grow.
So, I will definitely set a target rep range, and if I hit it and feel like I can get more. I'll usually rack it, and either add some more weight to the next set or just make a note of it in my workout log. Then next week, I'll be confident throwing more weight on the bar and maybe I"ll make a bigger leap than usual. That will lead to progress.
Training to failure sometimes isn't a bad idea. It can help push through a plateau. And some guys do it all the time. I think it's rough on your CNS though, and will burn you out eventually. At the end of my workouts, I like to throw in a lighter set that I"ll push to right to the edge of failure, or maybe failure. Doesn't kill me and gives me a little bit of metabolic work after heavy tension sets.