If you knew that your biggest table was 20mb, and you imported into a tablespace with a 20mb uniform extent size. Then you would only get one extent for each table. But it doesn't matter if you have more than one extent. My preference would be to have different sized tablespaces all uniform extent, with extent sizes of 1mb, 10mb, 100mb, depending on the actual size of your tables as well as how fast they will grow. If you use a uniform extent size, extents will always be the same size just like Jovery said.
Another, much more severe (a show stopper!) example of the potential problem when using COMPRESS=Y:
You have a table with 5 extents of 500MB each that was exported with COMPRESS=Y. Now you want to import this table. You have plenty of space in your destination tablespace, say 10GB, but this tablespace is composed of 5 datafiles, each 2GB in size. You won't be able to import it, since the initial extent will require 2.5 GB of space and an extent can not span the datafiles!
Jurij Modic ASCII a stupid question, get a stupid ANSI
24 hours in a day .... 24 beer in a case .... coincidence?