As others have said, a framing hammer is a specialty claw hammer.
So what makes it different? First, weight. A framing hammer is typically 20-32 oz, compared with 10-16 oz for a "normal" household claw hammer. That helps it pound large nails in only a few blows. Related to that is the much longer handle on a framing hammer.
Second is the face of the head: it's waffled to prevent slipping off the nail head, helping prevent bent nails. A regular claw hammer will sometimes have a textured face but not nearly as pronounced, and the face may also be smooth. A regular claw hammer often also has a domed face to allow a skilled hand to sink a nail below the surface with minimal surface damage: that's a feature you won't see on a framing hammer.
Third, the claw is straight since it is optimized for prying boards apart. A regular claw hammer is optimized for pulling nails.
If you're only building a garage, I'd recommend using your regular hammer rather than buying a framing hammer. (Or best of all, just go rent a nail gun!). For inexperienced carpenters, the time spent hammering will probably not be what slows you down. Also, the framing hammer is tiring enough that after a couple hours you may actually be faster with a smaller, regular claw hammer.
If you do get a framing hammer I recommend a lighter one. You'll work faster when you use it, you won't lose much power over a heavier hammer, and you'll feel much better on the second day. In 2010 if you hammer enough that a 32oz hammer makes a difference versus a 24oz hammer, you have a nail gun anyhow.
Usually, around the home anyway, there are other signs to let you know when you've applied enough torque. MarkD noted a common one -- when you see the screw head just go below the surface of the wood. In your fencing example, if you're tightening lag screws or nuts with washers, you'll see the washer start to sink into the wood long before you've applied enough torque to shear off or strip the screw or bolt.
It's a great tool for this kind of work, and it's super fast. Don't slow yourself down unnecessarily by underestimating your own ability to judge how much torque you've applied, and how much is enough for your application.
Best Answer
The pin/ball detent system is the more secure socket retention method. However they can be a real bear to release. They are especially tight when new sockets are used on a new gun. This is compounded if your hands are wet or greasy. The friction ring is still secure but lends itself to easier socket changes. So if you are going to install one socket and use it all day, over your head where it is likely to fall off the detent system is your choice. If you are using different sockets frequently where easy removal is important go with the ring retention.