I gather the main reason folk fit them is to prevent the engine's blow-by oil getting sucked into the turbo & getting baked on in places whee it is not desirable - ie. a means of keeping things clean & extending the turbo's lifespan.
Fitting a catch can wasn't something I had ever really thought about until I lifted my bonnet in the company of a couple of mates last weekend, both experienced diesel owners & mechanics, although not specifically with Patrols.
On opening the bonnet they both immediately commented upon the fact that I still had the 'suicide hose' fitted. I had no idea what they were talking about!
Turns out they were referring to the breather hose which goes from the rocker cover to the air inlet pipe between air filter & turbo. They explained that in certain circumstances, usually when giving the motor some welly up a hill, that it can become impossible to shut the motor off with the ignition key because the motor can continue to run on the 'blow-by oil, rather than diesel, after the fuel solenoid has cut off the diesel supply. Although rare, both claimed to have known of occurrences. When it happens apparently the only way to stop the motor is to block off air, not an easy task & fraught with the danger of injury as engine suction is extremely strong.
The suggested preventative solution was to fit a catch can mid hose to separate oil from air.
I have no reason to doubt what I was told, but in looking at catch cans I have seen no mention of reasons other than for engine cleanliness.
Nevertheless I have now bought one (a Provent 200 copy) & have spent this arvo making a bracket to hang it from.
Interested in any comments about what I was told.