Practically none. The only problems noted by technical support involve clean-up procedures sometimes necessary with some unbalanced equipment or “dirty chassis” gear. These are relatively rare and can almost always be fixed. (See Tech Support Bulletins: Audio Wiring & Grounding and The “Dirty Chassis” Condition.)
There are a few power sequencers that are incompatable with balanced ac. In every case, single pole on-off switches on the power sequencer were used to shut down the audio/video electronics. This results in 60 volts being fed into equipment power supplies via the unswitched balanced power line. It may be unusual to think that turned-off equipment can cause problems. But when a single-pole switch is used to disconnect the power, ground current leakage that would normally null is dumped on the ground. Furthermore, if the ground leakage exceeds 5 milliamperes, as a shock protection feature, the Equi=Tech will shut down. In one case, a studio owner reported that the GFCI devices on the Equi=Tech would trip overnight when his studio was shut down. This was determined to have been caused by single pole switching on a power sequencer. For the sake of functionality, it is recomended that 2-pole switches be used to disconnect equipment. At the Equi=Tech system’s outputs, the output circuits are switched twice with 2-pole devices, one is the circuit breaker, the other is the GFCI device. Either may be used to shut down electronics.
There have also been a few instances where some equipment either demonstrates little no improvement in performance or causes nuisance GFCI tripping. In many cases, the manufacturer has used an unbalanced “L” type line filter which is by design, unbalanced. Sometimes equipment modifications made in the field will incorporate .01 caps (line to ground) to filter out noise. This defeats the function of the balanced power system by leaking current into the ground. Most manufacturers use a “stock” balanced EMI/RFI filter which is wholly compatible with balanced power. If an “L” type filter is discovered, it is recommended that it be replaced by a “T” or an “O” filter or at the very least removed.
(Note: beware of modified equipment and extremely sub-standard power supplies that can also exhibit the same symptoms for similar reasons.)