They save no money. They are a decent answer to how few good IT workers are found amongst US citizens. Replacing US IT workers with H1B workers, however, is both counter to the explicit intent of the law and serves no purpose. The cost of sponsorship and the headache of the paperwork make this a bad choice unless there are no US workers you can find to do the same work.
Unfortunately, finding good talent among US citizens is getting harder over time. Seriously, if you are a US citizen still in high school please please please go get a STEM degree or seek out a STEM job. We kinda need you. It takes me months sometimes to find a qualified developer or system analyst for my open positions.