Laptop or desktop doesn't matter. And the size of swap doesn't matter as long
as you don't run out of memory+swap.
The access times for disk (swap) are an order of magnitude slower than
memory. Just like how the access to the various L caches the CPU uses are
again an order of magnitude faster than RAM. In the image below (of the
memory test suite that comes with Trisquel too, memtest86+) we see the sizes
and speeds of various memory blocks.
So computers have a little bit of really fast memory and then larger and
larger chunks of slower memory and then finally disk which are ridiculously
huge these days.
When you're out of memory and have to use swap and the computer is accessing
the disk like crazy and nothing seems to be happing this is called trashing.
If you intend to hibernate, you need (about) as much swap as you have memory.
(The image does get compressed, so not quite as much.)
Memory is pretty cheap these days. Having said that I only have 1 gig myself
and don't usually need any more. YMMV
