What would be the reason handling a frog?
Best thing for them is to be left inside their viv.
If you like a pet that can be handled, maybe a frog won't be the right choice.
Like already said, it puts the frogs health in risk while it isn't necessary at all.
Besides cathing out juveniles or for treatment i never get my frogs out.

The peeing actually is mostly water, just a very small percentage is urine.
It's part of the defence mechanism indeed.
By squeezing out the water they hold, they make theirselfs lighter and therefore they will be able to move faster and jump further.
The weight reduction can be as much as 50% of the total body weight.
In my point of view, a frog never gets used to handling, it's not like you can tame a frog.
Maybe the great amount of topics on sick, deseased, stressed or even death frogs could be because of the handling by most people,
reading the frogs are often taken out at least once a week for cleaning a cage, i guess it's not the most suitable way to keep them.
Stress is probably cause of death number 1, so you might like to avoid causing stress as much as possible.