A line which we want to shut off the steam to has no steam trap on it.  The line runs into a sump, where it just flows out of the pipe.  The valve is by the main steam header.
If the valve exits the header from a position lower than horizontal, there will be a pool of condensate between the header and the valve. 
Also, when you shut off the valve,the line will cool.  thermal contraction can make it move around a bit as it cools, and when you put it back into service you might want to just crack the steam valve gently to warm the line slowly and prevent thermal shock.  The bad news is that if the isolation valve is holding a pool of high-pressure warm condensate and you crack the ball valve open, the condensate will cavitate and damage the valve seats.  Next time you try to shut it off, it will leak. Leaky valves never heal themselves.

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