A lot of comments here have mentioned that inkjets don't perform well if left idle for a long period of time, but I can't seem to a reason for this. So, why?
The ink in the nozzles dry up and usually it takes several 'cleaning' sessions to get them all working again.
Yes this exactly. My friend has a professional printer like you'd find in printing shops, and when he is on holiday I go to his house every few days to run a test print to make sure the head doesn't dry up. If it does, the only real option is to pay a few hundred Euro for a new one.
The ink dries out on the ink heads/and then cartridge, where as toner is already dry and can usually sit unused for much longer and still work fine.