You get a valid warranty, the machine will work with your television, and if anything goes wrong, you can go to the shop and play merry hell with the staff. Outside Japan, people will always buy imported machines. Some people buy them because they want to play Next Generation titles nearly twelve months before they are released in their country or they wish to play the games as 'nature' intended, full screen and full speed. If you live in Japan, then you have no problems, the PlayStation was released there first so you can walk into any game shop and buy one. The television system is NTSC and your voltage is 100 Volts.
Life is sweet.
If you live in the USA or Canada, then you may have imported a machine from Japan to skip the 11 month wait for the US release or to play rare Japanese RPGs, which are apparently unappealing to Western tastes. The television system is also NTSC and your voltage is 110 Volts, which is nearly 100V, if you are concerned you can buy a extra power supply that gives 100V. You can plug in and go. Life is sweet. Your tv system probably isn't compatible with NTSC and your power supply is 220 - 240 Volts. Life is sweet as a lemon.