Personally I always thought it was surprising that Picard didn't use the ability a lot MORE. Especially in battle like we saw in BOBW, where you'd basically have two-ships-in-one and could flank the enemy and attack from both sides.
The saucer may not have had warp drive, but it did had some massive phaser banks to defend itself and attack other ships. And we've seen LOTS of Trek battles where the ships utilized nothing but impulse engines to maneuver around, so it's not like that's a new thing (hell, it's not like the Ent-D looked all that maneuverable even with
both halves together; that thing was always slow as hell).