Warp strafing
Warp strafing is a theoretical battle tactic invented by Star Trek fans. The tactic has not appeared in canon.
Theory
In the proposed tactic, a starship light-years away from its target sets a course to fly past an enemy vessel. It then approaches the target at warp speed. When the the starship is in range of the target, it fires its weapons, with the target unable to return fire.
Usage
Warp strafing has never occured in any Star Trek episode.
Elaan of Troyius is not a canonical warp strafe. Sulu counts down the distance between Enterprise and the Klingon vessel in tens of thousands of kilometers over several seconds, indicating the relative velocity between the starships is less than c. This incident is similar to any other warp battle in Star Trek, with one starship pursing another, both traveling faster-than-light.
The word impulse in Star Trek does not necessarily mean slower-than-light, as evidenced in several examples including Best of Both Worlds Pt. II where the Enterprise-D drops out of warp at the edge of the solar system and shortly enters Earth orbit, necessitating faster-than-light impulse. Elaan of Troyius is not an example of a true warp strafe, which would involve one starship at rest or near rest relative to another approaching faster than light.
The Picard Maneuver is not a warp strafe, as the Picard Maneuver specifically involves dropping out of warp before firing weapons.
Physics
The critical problem with warp strafing is relative speed. Suppose car A approaches car B while at 50 km/h. Further suppose car B is traveling at 49 km/h in the same direction. The relative speed between car A and car B is 1 km/h.
However, a car traveling at 100 km/h compared to a car traveling at 20 km/h in the same direction approaches at a relative speed of 80 km/h.
This is important because Star Trek starships of every faction have difficulty locking onto relatively slow and predictable targets. Attacking a vessel traveling many orders of magnitude faster than what weapons directors are designed for and capable of will not result in firing solutions.
In The Wounded, the USS Phoenix fires at a Cardassian vessel one light second away. However, even if the Cardassian vessel was entirely stationary and the Phoenix at warp, it would have been in range for fractions of a second. There is no evidence that this is a warp strafe, as opposed to the Phoenix firing at a stationary target while being stationary herself (see Stationary Targets). If it was a warp strafe, the Phoenix would have used only a fraction of its firepower for fractions of a second.
Starfleet Captains understand these limitations, as they never warp strafe.
Stationary Targets
Warp strafing would be ineffectual against stationary targets. If a target were stationary, the attacking starship fire torpedoes without the strafe. Secondly, stationary and heavily defended targets such as battle stations, weapons platforms and fortified planets could track the attacker with faster-than-light sensors. Any vessel attempting this tactic would move in a predictable straight line, a so-called "attack run." Unless the attacking vessel further complicates the attack run with changes of course and acceleration, the defender could track the attacking vessel just as easily as the attacking vessel could track it, with the added advantage of being stationary and using more power for shields and weapons.
Conclusion
In summary, warp strafing requires the attacker have more advanced propulsion, sensor and weapons technology than the defender. If this was the case, it is likely a more conventional approach would succeed just as well. The attacker could simply stay at stand-off range and pelt the defender with missiles, without the need for a dangerous approach.