Several times I have gone into existing electrical installations and seen EMT joints seperated, hanging, wire exposed, and the like.

95% of the time (or higher), set screw couplings were used.

When the EMT is installed properly, i.e., number and location of supports, pipe inserted ALL THE WAY into the connectors, etc., set crew connectors are fine, but -

Face it! Connectors do not always get tightened properly, conduit fittings ARE sometimes "cheated".

Even when a compression fitting is not adequately tightened, I feel it provides a better grounding integrity that an untightened set screw connector.

I am a union electrical contractor and electrician. I always prefer compression, even though it costs more in material and labor. In addition to reasons above - I do not like the "dimple" made in the pipe by set screws. And if the connector is later disassembled/reassembled (for whatever reasons ...), you have more dimples, or a dimple half way over another - definitely not a good connection ...)

The exception: On larger conduits (say 2" and larger), with the double sets of set screws - I have NOT seen these conduits hanging and/or separated. Price WOULD dictate set-screw over compression ...

However, other union electricians disagree with me and want set screw - I think mostly because they are quicker and easier to use.