Good fighter or bomber pilots can evade missiles at least 50% of the time, however they have a hard time shooting back when they are doing this.
I have an Orca and I mount one missile on the 360 degree middle turret mount for just this reason, to allow me some breathing room and to regen shields after being hit with a SNAC etc.
When going against pilots that have trouble evading missiles a single missile launcher is excellent to lower shields on a fighter/bomber and allow a fatal razor or main gun hit.
I've tried 2 missiles before and it's great against NPC's but I've found them a waste of energy against bombers and GB's. Energy better directed towards razors and pulses.
You also get criticized for using even a single missile mount sometimes... Which I think is silly. If you have weapons that are allowed to be on your ship and are effective you should use them.
Quote:La vengeance est un plat qui se mange froid.