OK,
Thermal imaging must be done under nominal or full load conditions to be of any use, doing it out of hours when the plant is shut down (for example) is worthless.
On fixed switchgear thermal imaging will highlight poor connections where excessive heat is being generated due to Joule heating, that is I^2R heating, the current is the current, thus it indicates connections with increased resistance.
As long as it is done correctly it does have a value in a maintenance regime.
It cannot replace physical inspections and electrical testing.
If one is getting changes for example year on year in fixed busbar systems, then you have a problem.
Changes in dynamically loaded & operated devices such as contactors there is more chance of detecting an operational failure due to say an imbalance, however, an imbalance across the contacts of a 3ph contactor could be due to a contactor fault, or due to a load issue.
So, all the thermal does, is say, look at xyz in more detail.
Is it valuable, yes, do I do it, yes.
You need to realise though that it realistically requires unhindered access to energised parts, so you need to be sure that the equipment is already in good condition prior to taking the covers off.
Done with sensible precautions it is safe, and a good tool, if you are insisting on dressing guys in full arc flash gear, then you really need to be looking at the condition and design of your systems before you look at doing thermal imaging, and having a ground up re-design, because the are not safe for use.
Keep asking if you want more info.