1. It's messy - I've always had to wash it down 3-4 times before it's clean
2. Can't use colour. Except for pastels. I don't do pastels.
3. It involves dark paint - which I wasn't willing to do in my apartment. Although Hudson Paints [see here and here] supply really great colours, the ones that really work and don't stain [they'll tell you this] are the darker colours.
So while perusing my local Dollarama - yes, I'm there several times a week - I came across my go-to wrapping paper of choice - kraft paper - and a light bulb went off. So, I scooped up four rolls [they're only $1 for a 12' roll, so go ahead and splurge] and a pack of binder clips [another $1] and headed home.
I pulled out an old curtain rod I had lying around, a couple of push pins, threaded two rolls of kraft paper on the rod, attached the binder clips to the rod and hung them from the pins. I rolled out the paper and prevented the rolls from unwinding by clipping on a paperclip [which is hidden at the back]. Presto! Voila! A wall I can write on. I also tied a piece of chalk to the rod with some charcoal yarn so you don't need to search for something to write with. What's great about the kraft paper - you can use chalk, crayons [yes, I own a full 64 pack of crayons], pencils, markers - it's recycled material - when you're done, just tear off the used piece and roll out a fresh section - and it's only $1 for a 12' roll.
Why binder clips and push pins you may ask? Because it keeps the paper tight to the wall - a regular bracket for the curtain rod would push it several inches off the wall which doesn't work very well for writing.. Alternatively you can use pegs and ribbons, but I like the look of the binder clips and push pins. Again - have fun with it.