I agree with most of the ...

I agree with most of the comments made prior to this one as to definitions.

Carry over is specifically any solid dissolved or suspended in boiler brine that becomes entrained in steam output as particles of solid material, micro-droplet mist, or generally wet steam.  Physical causes include poor level control in boiler drums, poor upstream treatment of boiler make-up water, especially where high silt/clay surface waters are the source, and failure/misapplication of boiler internals (mist eliminators).  Failure to use the correctly pure water for steam attemperation can also result in "carry-over" although this is actually resulting from direct contamination of the steam.  Anything related to carry-over must be strictly prevented in Universal Pressure Boiler, or once-through boiler as all the water entering is converted to steam.

The impact depends upon the application, thusly for heat exchange carry-over may result in impingement attack of surfaces, leading to failure, deposit accumulation also will result in loss of heat transfer efficiency.  For rotating equipment (bladed Rankine cycle turbines), deposits on blades will eventually spall off unevenly, and this gives rise to excessive vibration, or even sudden catastrophic failure of blade rows due to sudden release, gross rotor imbalance, if the problem is that severe.