IMO, ATS would be a very good helper, but for most cases, a nice size skimmer is still important.
1. To eliminate the skimmer, you will need a large ATS that may not fit in your stand. 105gal tank with medium bioload you may need 2~3 sqft or larger screen. So why not letting a good skimmer do 75% of the work and have a smaller ATS as a helper.
2. Ats is not stable. when its at its full growth, your nutrients may get too low that corals started to starve. But after you clean the algae, it may grow nothing for a few days and your nutrients may go up too high.
3. power consumption. a good size skimmer pump may consume 20, 30 watts of power. A 2 sqft ATS will need at least 100W just for lights (cfl), and you may need a large pump ( 700+ gph) to feed it, thats another 50~80watts.
4. Over heated. with extra power consumption, your tank is going to be over heated, especially in summer.