the problem is not so much that you will be causing a problem more than the ink, even though it is in a sealed package, will dry out some and can lead to clogged print heads .. but since most ink cartridges have the print heads built in, if they don't work, or stop working, throw them out then .. not before ...
as for toner for laser printers, they will absorb moisture over time and will not adhere to the drum electrostatically. This will cause problems if the toner is used for prolonged periods of time as it will require more frequent cleanings.
