A few things that come to mind:
1) Not flanking per se, but the area-of-effect weapons (some radial aoe, some linear aoe) make positioning more important in those cases. Particularly with the continuous beams on the Spire capital ships, firing enfilade into an enemy formation can be absolutely devastating, where if the enemy is more spread out you may only do 10-20% of the beam's total potential damage (or less).
2) Within a system, there are often angles of attack against specific targets that expose you to less fire and attention from other defenses in the system.
3) If you have some weak units with high range, maneuvering so that the enemy comes after your main force and passes within your high-range units' range envelope without having much (or anything) with the range to fire back can be quite good for kill-to-loss ratios. Of course, you can also just keep those units behind your main force, but that gives them less time to shoot. If you have problems with the AI sending attacks at those harassing units, using cloaking starships and/or transports can help.
4) Sometimes defeating an AI force in detail instead of letting it retreat can save you significant pain later on. In human territory you'll probably have a sufficient speed advantage to simply overtake them, but with some unit types or in neutral territory (attacking a blob of stalking threat on your borders, etc) having an attack force to hit it on the retreat can make a significant difference. You can even get pretty brute-force by using units with tractor beams.
But yea, there's no restrictions on turn speed, firing angle, different defenses at different angles, etc. So most of the heavy tactical stuff is abstracted out.