Wise disk parting.

[Strong]

I want to get the list's advice on disk partitioning.

I have a laptop with 74Gb hdd. At the first I thought to partition it
having single partition on it - it is very useful - no need to look for
the free space of a partition - if whole disk is full then it is full -
unlike with  several partitions on it - when it is necessary to move
data from one to another just to have the necessary sum of free space.

Then I sought on defragmentation of fs, that it would be much less
defragmented/higher_performance/longer_hdd_life if I divide the often
changable data from relatively constant - that is the OS files from
var/home/other_storage dirs. So, I decided to use at least 2 partitions.

What is the list opinions and arguments on this matter regarding what
have been said? Big thanks.