cfsindorf

IIRC
Pros. Can hide outlet's within rockwork, can have infinite number of outlets
Cons. Lots of piping and drilling, can be noisey, cannot change flow as easily as with power heads

That's pretty much it. If you have the room to run all that plumbing, it's nice. However with the higher end equipment on the market today, a closed loop has quickly become obsolete due to electricity consumption. Take a single pump that moves 3600gph at 160w vs. a Vortech moving 3000+gph at 28w.

If plumbing leaks, you have to repair it immediately. Vortech and Tunze pumps keep the water in the tank.

Some additional considerations:

If plumbed correctly -CL pump replacement is clean, quick, and dry. No getting into the tank. Closed loops likely contribute less to heat in the tank -

And, somewhat dependant on the size of the tank - I like CLs for large tanks (5 plus feet in length) I lave many Tunzes and 3 Vortechs. They do not move the volume of water as far as I would like. They are great - but have limits too.
And - the potential of stray voltage or current leakage is always present when you have a submersible pump in water. It is just part of the trade-off. Again, I use them, but I limit the number of them for the above reasons, and utilize a CL when the sytem is large
T

I knew it would not take long to get an answer here. You guys n gals are great

I love having a closed loop. I do have a vortch but even that in my tank bugs me. I hate equipment in the display. You can always cap a CL if you dont like it but you can never add it once the tank is set up. (a drilled cl I should say.)