Just like fire needs oxygen, heat, and fuel, cars become roadblocks withoug gas, battery, and air.  You can carry more gas, and a second battery / electrical system, but air is hard to find, and with "service" stations removing it from their offerings of yesteryear, you need to have your own air system.What impressed me most about this compressor was the attachment point to the valvestem.  It is threaded and screws on, forming a seal during refil.  This seal is exceptional - good enough that the guage mounted on the compressor itself is accurate to set your tire pressure at the other end of the hose.  If you are filling a big tire, it will take some time, so this lets you sit back and relax while the motor works.  My tire chucks for shop air all require constant finger pressure to ensure a seal - not having to get tire chuck thumb was a nice side benefit!As for portable inflation systems, I've grown tired of anything with a cigarette lighter plug as the power source.  It's limited to 10 AMPs which gives you roughly 130-140 watts of power.  740 would be a full horsepower.  This compressor under load can draw 30 amps at 13V, for 390 watts - more than a half horsepower.  To do that they use clipon cable back to the battery.  Because I carry a second battery I clip on to it for the juice to run this.  It will also work with your main starting battery if you don't have a backup elecrical source.In the box you will find a carrying bag as well as an octogonal shaped piece of plastic - thats the air input filter - you need to screw it onto the air inlet to protect the compressor.  Its a quality unit so it needs protection.When all is said and done you have a 1/2 hp 12VDC compressor that gives you the freedom to set your tire pressure when and where you want to.  With the fast fill rate it takes very little time to top off your tires, if you want to drop your pressure for sand offroad and then refill it later when you hit asphalt this is a small but valuable tool to have in your emergency kit.The unit has a well balanced carrying handle to take it between tires and is light weight enough to take with you everywhere.  While you can use your car's starting battery, a second battery will prevent you from draining your starting battery.  When done, start up and drive away.If you seriously go offroad consider a highjack lift to get you out of a bind, or else a hydraulic system with a portable cylinder fed from your engine's hydraulic pump (if yours is equipped with one) or a secondary hydraulic system powered by your secondary electrical system - with all this you will not be stuck for long!Finally maintaining your tire pressure at proper levels for your load optimizes your fuel efficiency - at $3+ / gallon for fuel these days your efforts will pay for themselves shortly.While I have a 240VAC compressor in my shop, this is the first honest 12VDC compressor that does not take forever to fill a tire.  With a half horsepower air cooled motor it does the job quite well.  It's worth the money to keep onboard.