Making a star ship with broadsides, stern and bow seems so impractical. Wouldn'the the optimal space ship design be a sphere? You could fire everywhere and turn on a dime, and you'd get the best possible structural integrity. Kinda boring though.
Generally, no. It's perfectly good if you're the most powerful thing around and can afford to have your entire battle plan being "I'm just going to plow straight through any hostile fleet with no regards to anything." So it's great when you're the Borg, who literally do just plow through fleets and just not care about the nuisances poking away at it from every side.
For everyone else, you're generally not going to be sitting in the middle of enemy fleets whenever you get into a fight. You might be fighting one on one, or against a fleet, but either way you're generally going to be keeping them in as few directions in regards to your ship as possible, which makes spheres or cubes a problem; only half of the ship can ever target another ship with direct fire weaponry. A pyramid shape on the other hand will only have one side that cannot fire on a given target, and if you flatten the pyramid into a dagger shape (Star Destroyers), you decrease the frontal target size and the space at the back that otherwise might not be doing anything, but keep roughly the same amount of guns on the target.
The other thing to remember is that spheres and cubes will have quite a bit of internal volume for its surface area, which might be perfectly fine or bad thing depending if you need that space, but it does mean more weight. A dagger/arrowhead shape will have much less volume compared to surface area, allowing for more weapon/sensor/thruster/etc emplacements for the ship's mass and size. So a well designed dagger shaped ship might be considerably more agile than a spherical ship while bringing far more weapons to bear. Even if the sphere comes at the dagger from above/below/side, the dagger still has the same number of guns on target as the sphere. The sphere only really gets an advantage when it comes from behind, but that's less likely since the dagger is probably more agile.