Vickilee,
I think in a fish only you should have a skimmer, but if you do go to a reef set up, IMO, it's optional.
The corels can benifit from the "dirty water". I now only run a refugium, LR and a DSB as the only means of filtration. My tank looks as healthy as one running a skimmer. I had a bout with some hair algea, but it is skrinking in size rather than growing. I believe that is normal to have some kind of algea problem with any tank as things stabalize.
You must remember that a skimmer can remove not only organics, but also small pytoplankton and other stuff you may want in the closed system.
This board will give you different opinions as will different "experts".
Do you have alot of fish in your tank? Any corels, mushrooms? How long has the tank been setup? Have you had any probelms so far that would make you think you need a skimmer?
How about nitrates and phosphates, what readings do you have?
How often do you do water changes.
Don't think I'm trying to get you to buy one or not buy one, just that you should look at how the system is running now. If it's not broke don't fix it.
HTH
D.Burr