From my chest of nuggets that I find myself want to repeat every time I watch somebody else's replay including those of the top "pros"...
On really important worlds (choke points etc.) that you haven't taken yet, it's best to leave scouts "in orbit", i.e. with an approximately circular path plotted around the outer edge of well, thus avoiding the enemy militia still present, which is possible because the scout is faster than any of the combat ships. Simply moving a scout between planets doesn't work as well because you can miss an approaching enemy fleet if it [cross] jumps while the scout is jumping in the opposite direction; if the phase lane is too long you can even miss them entirely as a back-and-forth jump on a long lane can take longer than crossing a grav well, which the enemy may well do if goes for a [short] run through the well without fighting the militia. (Typically this happens at planets that are expensive to colonize early on, e.g. Oceanic.) The back-and-forth-between-wells scouting method takes less time to plot than the circular path though, which as I said elsewhere before, needs to be a dodecagon (12 corners) for the scout to maintain its speed while negotiating the paths' corners; you can plot coarser approximations of a circle, but the scout will then take damage at corners as the enemy temporarily catches up and the scout will eventually die. But even with less effort/time spent on plotting a smooth orbit for it, it may still last long enough (minutes) to provide useful early warning.
Given the importance of the maneuver, "orbit planet" should probably be a one-click command in the scout panel (like auto-explore) but I guess the devs missed the importance of continued early warning at (well) chosen locations. If you do this in single-player, beware that the AI is so inept at dealing with the orbit maneuver [done manually] that it's basically game breaking if you pull it on early AI fleets (instead of militia), stymieing their advance for tremendous amounts of time (like they hit a SB sans the losses), unless they somehow manage to have fighter cover, which the AI seldom does early on (AI wuvs battleships as caps). So I guess "orbit planet" is really something the devs haven't considered because some factions have research-based substitutes... which gets me to the fact that except for TEC's Probe there's really no acceptable substitute for this maneuver, and Probe costs what two scouts do, besides competing on the same timer as all the early econ research that TEC should do, so Probe is not that appealing early in the early game (15 mins or so) even on the fast/faster research setting (which halves what "normal" research times are).
Besides location based early warning, keeping tabs on the main enemy fleet, while not as important as (say) in the WWII Pacific carrier battles, still provides a significant advantage in Sins. This is ironically most important as the Vasari (which get no research-based early warning system) because of Vasari's dependence on deploying and upgrading a SB on the right planet at the right time in order to be able to withstand the incoming enemy fleet.
The Advent (which have a pretty crappy "Lingering Presence" research [IIRC] that sorta acts like Probe after the scout's death) also get a moderate benefit from early warning because their hangar, which is more expensive but also more durable than other faction's hangars, once upgraded with shield bestowal (also a pretty expensive L3 research early on) makes for increased durability of all structures around it, thanks to shield mitigation. So knowing where deploy a hangar [and repair platforms] and when to research shield bestowal to buy time for cavalry to save the day also helps as Advent fairly early in the game.
