resource usage concerns

Technically most applications have a few pieces of data that won't be accessed in the future but are still kept around, e.g. if you have an object that stores all your command line options including the listen IP and port and no restart mechanism those values likely won't be needed after the initial bind but will still be kept around.

A more elaborate example might be a work queue where a priority field is only used on enqueuing but still kept around until the task has been processed to completion.

Mostly that falls under your "is large enough to care about" but in general it is just a trade-off between being worth restructuring your entire application data structures to be able to free pieces you won't need independently and the amount of extra memory used.