Even if you are about to die, just don't touch with pit if you want your phone to be okay.

Bro you are giving wrong advise and is totally wrong. care to explain your point before i say mine
Understanding PIT file is important - just simply ignoring it is infact dangerous
The horror stories some read is simply because users do not understand and use the wrong PIT assuming is same for all firmware in different regions - these happen to frequent rom flashers who just ignore PIT

I was waiting for the user to respond to me before I reply. He was making a generalized statement which is misleading. ANyway here is my understanding . First and foremost I am not an expert in such stuffs - this is based on my experience flashing the first Galaxy S and Galaxy Tab and present Galaxy S II.

PIT stands for PARTITION INFORMATION TABLE. The pit file basically tells Odin how to divide the partitions (for formating) and also where certain components ( PDA, PHONE, CSC ) to go when flashing them individually. PIT understanding is very crucial when you wish to flash roms from samfirmware.com , one place I always discourage new users from attempting as it is a trap to bricking a phone if you do not understand what you are doing

Cooked roms take cares of PIT ; you rarely see cooked roms asking you to choose PIT during flash thro Odin. Most cook roms, the developer has built in his rom the PIT instructions

For example, in the samfirmware.com Galaxy S site, you can even see different types of PIT listed and a warning that you choose the right PIT file. In its SGS II site, If you look at samfirmware.com - there is a default PIT file you can download at the top box just above the list of firmwares for different regions. If you download any of these official roms, you will see some roms comes with a PIT file and some does not. You asked a very good question, why is the PIT included if is of no use ?
My advise is simply this : If you see a PIT included in your rom, choose it during flashing as most probably the PIT is a changed version from default. You can only use this PIT to flash with the rom that comes with it. You cannot take this PIT and used it to flash another rom - this will brick your phone. When you use a wrong PIT - you have 2 possible scenarios :
- failed flash and phone cannot boot
- flash OK but the whole internal SD is formatted and cannot be detected at all by phone ( my experience with the Tab)

If the rom downloaded does not supplied a PIT file - than you just flash it without it or you choose the default PIT

As the PIT name implies, using PIT basically repartition /reformat your whole internal SD - once you select PIT, you will see repartition is auto selected. All your data in the internal SD will be wipe clean

You can choose NOT to select the PIT during flashing if you wish to have your internal SD intact. I cannot say whether you will have a successful flash. If is successful it just means your present rom PIT is similar to the rom you have downloaded. If is unsuccessful, just flash it again and select PIT

Read this post if you wish to know more. The writer similarly points out about the false/wrong understanding of many users about using PIT
http://forum.xda-developers.com/showthread.php?t=999097