There are several related links here . Again, if their absolute luminosity is known, their distance from us can be deduced. They can be used to measure the energy density of the universe, and the cosmological constant. Large scale structure refers to the distribution of matter on very large scales in the universe, around and above 10 Mpc. The relation of the hydrogen clouds to other structures at different redshifts is schematically pictured by Z. Haiman.
Galaxy clusters can also be gravitational lenses .
Weak lensing as above can be used to study large scale structure. The picture source is here . The photons have the imprint of what the charged matter was doing right before decoupling, as well as the imprint of the gravitational potential they have travelled through in the subsequent 10 billion plus years to reach us. The very small size of the fluctuations in the CMB means that calculational approximations are well controlled, and the resulting predictions are consequently very accurate. Follow these links for a list of upcoming experiments and in particular satellite experiments.