Sometimes, especially after I deadlift, the prospect of pulling the plates off the bar and carrying (rolling) them back to their place seems an unpleasant chore. I work out in my garage, so leaving the weight on the bar does not inconvenience anyone but myself. I don't leave it racked, I feel like a loaded barbell lying on the ground should not be under tension, and should be fine. Are there other concerns I'm failing to consider?
When on the ground the load on the bar is negligible. Since you asked to consider all concerns then you should know that when you have dissimilar metals in contact one of them can experience accelerated galvanic corrosion. How pronounced the effect depends on the specific materials in your equipment and your basements conditions Dissimilar Metals in Contact Chart.
It won't do much damage to the bar. The bar is your case supported on 2 ends, rather than it's weight distributed all along it's length. Bar is just 45 lbs, and it's not carrying any additional weight, when the plates touch the ground.
Having said that, if you rack the weights on a bench press bar raised above the ground by the support, the load on the bar would be immense, which is equal to the bar's load and load of the plates. The concept of moments in physics applies to it.
It depends on the building quality of the bar. A normal oly bar is rated for about 400-500kg, so if you leave 100kg on the bar in the squat rack and there is no noticeable bend to it, it's going to be fine.
I have a quite cheap bar at home, where I frequently leave 90-140kg on it in the squat rack. 7 years later and the bar is still fine.