I think it depends on the individual. Some people need to stay as close as possible to being in the same position in bed while recalling, which is why keeping a notebook by your bed can be really handy, as opposed to getting up, turning on the computer, opening up whatever you're going to write in, staring at a bright screen, etc. I've found it doesn't really matter for me - but when I first started recording my dreams I used a notebook and then later rewrote them on the computer. I actually really like the process of writing them down twice because even more can come out the second time around.