ExecStart lines for each tunable to be overwritten/ignored, after the inital powertop --auto-tune.
Firstly, find the default value by cat out the path/parameter.
Example (disabled the min_power suggestion)
ExecStart=/bin/sh -c "echo 'max_performance' > /sys/class/scsi_host/host0/link_power_management_policy"
Interestingly, the above mentioned auto-tune tunable seemed to be causing issues with a Crucial CT500MX500SSD4 fitted into my Dell 7490 laptop.
Intermittently, segfaults would occur with random applications (google-chrome-stable, firefox, nemo, sudo, etc.). Also various packages would complain about missing symbols (for example, running sudo mandb).