All motors have blowby. Boosted motors have more blowby.

The stock Positive Crankcase Ventilation [PCV] system functions okay...on a stock motor at stock boost levels; which creates a 'stock' amount, or volume, of blowby.

As a motor wears, or if the boost levels are raised, the volume of blowby will increase. If the size of the venting hoses is not increased as well, then two things will occur:
...an increase in crankcase pressure, usually resulting in seepage/wetness around seals and gaskets
...the velocity of the blowby gases through the venting system will increase, impairing the ability of the system to precipitate out the oil droplets from the crankcase vapors.

When THAT happens, you can see where that oil ended up going: back into the motor via the intake manifold.

...on an NA motor, you'll find that the throttle body is all oiled and crudded up.
...on a boost motor, the turbo compressor wheel will look oily, the intercooler will become an oil repository*, and the throttle body will be oily and crudded up.

[*when you remove an intercooler, and drain it, and have a quart or more of oil come out, it is a good indicator that the PCV system is not able to keep up. BTDT]

Increasing the size of the flow path for the crankcase vapors...bigger hose or more hoses...is the way to accomodate the increased volume of blowby. But that is only part of the solution.

Adding a catch can to the venting system provides:
...another place for the oil droplets to precipitate out of the crankcase vapors, and a place to store that recovered oil.
...the accumulator function that a catch can provides helps to reduce the amount of oil being ingested into the motor.

The reduced ingestion of oil is a good thing: ingested oil reduces the octane capabilities of the fuel being used. i.e., ingested oil can lower the detonation threshhold.

And THAT is something that is not good in a boosted motor.