At least in my observation and experience, 33s rarely if ever get into a situation where steering becomes impossible. They aren't large enough to create enough contact with the ground to cause resistance. They aren't large enough and the builds typically aren't capable enough to get the Jeep into the kind of trouble that stops the steering.
35s really changes the potential for that. And the further you push the build and also make use of the capabilities, the more likely one is to discover the steering isn't working right when it needs to.
I never felt like I needed hydro on 33s. Now on 35s, I have found those many moments many times.
I have noticed often enough at full articulation with the driver's high and passenger low, the drag link is at a steep enough angle that the leverage off the pitman arm is reduced to the point that the steering quits working.
While not a specific example of my steering not working, this type of twisting is where it can happen. Weight shift and traction only make it worse.
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Many can and do get away without hydro assist. But it becomes very clear when it would be very useful to have.
Hydro assist is definitely on my list of things to do.