Do they make traveling safer or more dangerous? Good question - and the jury's still out on that one! I've heard about horses having bad experiences with travel boots, but I've also heard about horses having bad experiences with everyday stuff like headcollars, rugs and haynets, and most of us don't think twice about using those things.
Have I seen a horse being saved from injury because they were wearing travel boots? - yes, many times. Have I seen a horse get injured because they were wearing travel boots? - no, but sometimes I think I can see it coming! I've lost count of how many times I've seen people using boots which were the visibly the wrong size/shape/style for their horse and/or not fitted correctly, that to me is risky. I've also seen people leading/loading horses in boots that the horse was clearly not happy wearing, that to me is risky also. Some horses don't like them and in those cases you are better off going without, or bandaging instead.
As I said on the other thread, if I was travelling a horse like Ben who had nice hairy legs for protection, I don't think I'd bother using boots. Same as I don't use them on Dessie and Mouse as they are so fuzzy, and the youngsters and broodmares don't wear them as they live out and have hairy legs also. But we travel the showjumpers in boots because they have fine legs and not much hair to protect them. They travel very regularly and spend hours on the lorry, so they're used to wearing their leg protection, and are clearly comfortable in it. The reason we opt for the leg-wrap kind rather than the traditional chunky padded kind is that they are usually easier to fit correctly and tend not to move around like the chunky ones. When I was in the middle of loading Jam the other day I got called to help a livery in an emergency so I chucked him in the lunge pen... something wound him up and he spent the next five minutes zooming around the pen bucking and twisting and leaping around, and his boots did not move an inch.