ORIGINAL: HEAD0001
2. Can be set up with more elevation and windage adjustment. Notice I say can be, because some are not.
3. Will allow more light transmission through the scope. You have to have the quality of lenses and coatings to take advantage of the larger tube size.
3 is the same as 2. Ifa maker gives you lots of adjustment, it is because the internals are 1" size or similar. If it has little adjustment, it is bigger to allow more light through.