The ‘parallel stations’ are mainly intended for non-sprinkler stations — now that OpenSprinkler supports radio frequency (RF) stations (such as remote power sockets), you can use it to switch landscape lights, or other general-purpose powerline devices with OpenSprinkler. Obviously these stations should not be serialized with sprinkler stations, and should be allows to run in parallel. So the ‘sequential’ station attribute is configurable mainly for that purpose.