To the people knocking the 45 degree Bent Over Row or the Yates Row (same thing), I think you are ignoring a potentially great exercise. As I see it is has the following benefits:
It allows for a large amount of weight to be used, it will probably be your strongest back exercise. This is a good thing, not a bad thing. As Tate and others have mentioned, a good way to see if your upper body pull and push are in balance is if your 45 degree row is basically even with your bench press.
It does not put much stress on the lower back unlike the 90 degree row (which is also excellent). If you are deadlifting heavy and doing heavy 90 degree rows (and squatting heavy) it can be hard to place those in a routine without overstressing your lower back.
The movement you are producing is shoulder extension which is a primary movement of the lats so don’t think the lats are not working in this exercise, they are.
You can do the lift supinated or pronated, supinated places a good deal of emphasis on the biceps much like a chin-up. The 90 degree is almost always pronated.
It is easier to cheat under control with the 45 degree row. This is also not bad. There is no spot on a bent over row (at any angle) so you can spot yourself by using your legs with a little leg kick. On a 90 degree row this can tax the lower back too much. Watch Pumping Iron again or almost any lifting video of someone going heavy, a little body english to lift more weight and place more emphasis on the target muscle is a good idea assuming it is within reason.
I agree the ROM is not as good as a 90 degree row but it is not that bad if you are truly bent over to 45 degrees, it should be about the length of your thighs and it is probably similar to the bench press stroke which no one seems to complain about. Again a shorter ROM equals more weight which is good, not bad.
Getting good at this exercise will help you perform most other back exercises because they will all seem relatively light compared to this one since the weights are heavy. If you can do 315 at a 45 degree angle, 225 won’t seem so bad at a 90 degree angle.
This exercise was a staple for both Dorian Yates and Ronnie Coleman (among others) which should say something.
I agree you can stand too upright on this exercise and if you cheat too much you can take away emphasis from what you are trying to work, but that is the case with basically any exercise. If you decide the 45 degree bent over row doesn’t work for you, that is fine, but to dismiss it as a non productive exercise is, in my opinion, not giving it its due.