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Engineering is one of the most expensive and time consuming professions in WoW. It is also one of the most fun and useful. Engineering allows the user to create machines and gadgets from metal, stone, and a variety of other miscellaneous items. You will want to pair this with mining so you can gather materials to craft with. It's beneficial to almost any class, but especially hunters and rogues. Because most of the engineering items are BOP and almost all of them require engineering skill to use, it is probably THE hardest profession to make money with. A skilled engineer can create many powerful weapons and useful trinkets to use on their quests. Some of my favorite engineering items allow users to breathe underwater, summon mechanical dragons or chickens to attack with, mind control enemies, resurrect allies, blast open locked doors and chests, teleport across the world, stun enemies, parachute, heal yourself, turn invisible, and fly. It's one of the most fun professions to master, but don't pick it up expecting to get rich from it.

This is just an opinion but Engineering loses its usefulness once you get to the better end of level 70.

 As a hunter  that likes pvp more than raiding I chose it mainly for Rocket (http://wowhead.com/?item=23836) and Surestrike Goggles http://wowhead.com/?item=34356 but they only last you a small amount of time, they'll get replaced easily once you begin raiding.

 

What i'm saying is engineering is useful but only to a certain extent. 

That's quite true. Most engineering items do set amounts of damage or have certain stats. You get them all based on engineering level, not character level. So say an exploding sheep can instant kill enemies at lv 10 so it's amazingly helpful, but once you hit lv 70, it barely scratches your foes. There are some things that are always fun and useful, like the shrink ray, mind control, and battle pets. No matter what their damage, when a caster has a dragon and chicken hitting it repeatedly, it has so much spell interruption it can't cast. Also in an instance, hunters with jumper cables can save a raid. You just play dead, wait till it's clear, then jump up and resurrect the healer. Most of these items give just a tiny advantage, but it can be the difference between life and death.

I totally agree with this. I have a engineer and while i haven't leveled it up yet, Its still very fun. Its also useful when you have the materials required to make everything, which is one of the bad parts of engineering.