At present db.currentOp() by default shows replication-related threads such as:

"WT RecordStoreThread: local.oplog.rs"
"rsSync"
"rsBackgroundSync"
"ReplBatcher"

Often these operations are long running and users may get a wrong impression that there is a performance problem.

As these can be considered as system operations, it seems reasonable to show them only if {"$all": true} is specified.