Not by enough to stop pretty much the entire population being infected, which makes it a very questionable benefit. Mostly they just spread out the period over

Not by enough to stop pretty much the entire population being infected, which makes it a very questionable benefit. Mostly they just spread out the period over which everyon gets infected and that has some obvious downsides itself - the effectiveness of the vaccines against both infection and death declines rather too quickly, meaning that delaying infections can in theory lead to more deaths. As I understand it slower spread should make it easier for more infectious and vaccine-evading variants to evolve too since each intermediate step in their evolution has more of a chance to get established and outcompete the existing variant, but vaccination is still sold as a solution to the problem of new variants as well.