in a proper 2yrly checkup they will look at your macular through your eyes. it is on the back of you eye on the retina. the photo they take is great because they can compare images each time they do it.
i work at opsm and take the photos for people. it is very interesting. im not sure if specsavers do the free ones every year or only when they can bill the 2 yrly check. we bulkbill for the rest of all the other tests we do. medicare are not subsidising the photos yet. at opsm you can also ask for the photos to be put on a cd for your own filing.
also we use a different camera which is a canon and use the same technology in the canon eos. apparently it is better... not sure though
the puff of air test is to test the pressures in your eyes. that is to do with glaucoma.

any other questions please feel free to ask