Well if you use minimum extent 128K no matter what initial next you are specifying in you table/index creation storage parameters they will ALWAYS be multiple of 128K.
For example if you set initial of a table 400K and next 200K Oracle will actually allocate 512K and 256K the advantage of this is you always get same multiple size extents therefore you tend to get uniform extent sizes.

And if I was using 32bit OS I would forget about 3GB file since 2 to 32 is 2GB, size limit for 32 bit OS