does it make a difference if it is used heavily instead of never being connected to system?
This point is the only one not covered by other answers so far.
A drive in use is going to see more wear and tear on the physical mechanisms (i.e. the head moving apparatus and the spindle motor) and is exposed to environmental conditions (changes in operating temperature inside a machine for instance, and increased chance of physical knocks if it is an external drive).
Inactive media may still degrade over time though. Changes in environment (mainly temperature for hard drives, humidity too for tapes) can cause the magnetic storage to slowly degrade as can exposure to other factors in storage (local magnetic fields, temporary or otherwise, contaminants in the air, ...). Also you may find that a drive that has been powered off for a long period of time will fail to spin-up once reconnected due to mechanical parts having "seized up" - there are techniques that sometimes rescue a drive from this long enough to get the data off onto another drive but they are not reliable. I've only every had one drive fail in this way, and I managed to get it going with the risky "quick spin" technique but it does happen. So if you are storing data on drives for a long time, store the data on at least two drives and test them occasionally (though that applies to any other medium too, not just drives - don't just store and forget if the data is important).
Lifetime and reliability measurements for hard disks: https://github.com/linuxhw/SMART/blob/master/README.md
– linuxbuild – 2018-02-19T10:44:03.963