[morzh]

Well, extra safety does not hurt, but of course an IT does not give you a guarantee of not being fried. One could die from an AA battery. If he swallows it.
This said, I always start with IT, and then if it is an AA5, hot chassis or not, I keep it on IT, id it is a transformer set and I know it works and the transformer does not leak/short, then I could use it directly.

BTW. Speaking of AA5 that are not "Hot chassis" - the chassis and the electrical common are linked with a capacitor which in case of Philco 46-250 I just worked on is 0.2uF.
0.2 uF will give you a touch current of 9mA.

Now according to the safety tables, AC touch current is like this:

Startle - 0.5mA (hand-hand, hand-feet, hand-seat)

Strong muscular reaction
- 5mA (Hand-hand)
- 10mA (both hand - feet)
- 5mA (hand - seat)

Which is non-lethal for most people. (the least deadly current is 40mA both hand to feet).
But then what if you wear pace maker, have a weak heart etc.

I say, IT is a good thing, especially with non-transformer radios.