Is Partitioning external hard drive necessary

What is it you are doing ?
It is good to have OS on one partition, other partitions for say, pictures,
movies, personal docs, downloads etc.

What is it I'm doing? Simple computing. Quite a bit of data.

I'm going to reformat my old laptop to speed it up. So i need to back up the whole laptop HD into an External HD first.

My external HD (ITB) is bigger than my laptop HD (250GB). I'm using only one OS (Windows Vista), may try Mac OS X in future. As such, what's your recommendation?

Some say partition is not necessary & may slow down some process (such as defragmentation??). I don't understand that.

Is it important to separate "system" from "data", therefore the need to create a separate partition for each? One expert says "Partitioning to separate system from data tends to be a tad error prone as many programs still insist on storing things on the system drive, but it can at times be a useful way to organize things."

If so, will the process of "backup data only" be faster? Will there be extra work to do? I'm really lazy. I hardly back up my stuff but I'm going to develop this good habit from now on.

What's the best way? Partitioning? At what proportion? 500GB+500GB? Bigger F, smaller G? What's your recommendation?

Help! I can't decide.

What is it I'm doing? Simple computing. Quite a bit of data.

I'm going to reformat my old laptop to speed it up. So i need to back up the whole laptop HD into an External HD first.

My external HD (ITB) is bigger than my laptop HD (250GB). I'm using only one OS (Windows Vista), may try Mac OS X in future. As such, what's your recommendation?

Some say partition is not necessary & may slow down some process (such as defragmentation??). I don't understand that.

Is it important to separate "system" from "data", therefore the need to create a separate partition for each? One expert says "Partitioning to separate system from data tends to be a tad error prone as many programs still insist on storing things on the system drive, but it can at times be a useful way to organize things."

If so, will the process of "backup data only" be faster? Will there be extra work to do? I'm really lazy. I hardly back up my stuff but I'm going to develop this good habit from now on.

What's the best way? Partitioning? At what proportion? 500GB+500GB? Bigger F, smaller G? What's your recommendation?

Help! I can't decide.