You can use the grips to add modifiers to, say, the face buttons to double the number of actions available to those buttons. You can use either trackpad as a “touch menu,” and you can assign nine actions to it (or double that with a grip modifier). It feels more natural (to me, anyway) to use the right trackpad as a mouse than it does to control a cursor with an analog stick. You can use the gyro for steering if that floats your boat.
The Truck Simulator games don’t have TONS of bindings to where you would want every option available to you on the Steam Controller, but they do include a lot of “administrative” stuff, like interacting with your GPS thing, and non-navigation-related functions, like the wipers and brights. If you like granular control, you run out of Xbox controller bindings pretty quickly, which is why most controller setups have toggles (like, Y turns on headlights, then again for brights, then again for off) instead of a binding for headlights, a binding for brights, and a binding for off.
The toggles are perfectly usable, but it doesn’t let you, for example, flash your brights at someone. (Not that that ever matters in normal gameplay, but sometimes you really want to immerse yourself in the fantasy). It all depends on your tolerance for doing the initial configuration.
(Personally, I LOVE fiddling with the Steam Controller configurations, but I can practically hear people’s eyes roll when I tell them it took me an hour to come up with the perfect setup for a particular game).