How much "Load_cycle_count" can my hard drive hypotethically sustain?

Most newer hard drives are good for 600,000 load cycles. In practice, you can usually do more, but the risk of hard drive failure is significantly increased. The reason for this is that continued wear to the head parking mechanism could eventually result in damage to and failure of the read/write heads themselves.

Turning off APM will stop the repeated load/unload cycles, at the cost of increased heat and power consumption. The following comes from my answer to the Server Fault question "Is my Hard Drive Failing?":

[...] This is typically caused by the Advanced Power Management (APM) feature, which tries to conserve power by parking the heads (unloading them from the platters) after several seconds of idle. The heads are loaded back onto the platters when needed. On most systems, where hard drives get intermittent, on-and-off activity, this can cause lots of load/unload cycles to occur. To turn APM off, run the following command at a root prompt:

smartctl -s apm,off /dev/sda

This command will need to be run each time the system is power-cycled or put to sleep or the drive is otherwise powered off, as this setting is not retained when the drive is turned off.

In my experience, doing this will dramatically reduce the number of load/unload cycles and consequently the chances you'll experience this sort of failure again in the future. Do note, however, that doing this increases power consumption and drive temperature. If the drive constantly runs at temperatures in excess of 50 °C, the risk of premature failure is increased, so you may want to leave APM on (or turn it on if it is off) during the warmer months.

I use the Blue 1TB HDD in a server, running since about 4 years 24/7 and till now it has 4,5 million Load Cycle Counts! No problems till now! I'll let it run until it starts to fail.

I currently have a couple of old WD20EARS disks that reached over 2 million load/unload cycles. Still work round the clock in RAID.

This parameter is not the only indicator.

WD Black/Red series will probably live longer than WD Blue/Green but it's not entirely due to a different firmware settings, but build quality.