I always bring an umbrella and I use a GoLite Dome. I feel the extra 9 ounces I carry with that umbrella is well worth it. I also use two collapsible trekking poles (mostly for rhythm and shelter support). While there have been occasions I needed to put away one of my poles, to free up a hand to hold the umbrella, it has not occurred often (I think twice, maybe three times). We don’t usually see much rain until the late afternoon thunder showers when they are in season. That is also about the time the scouts want to be setting camp.
With a group of scouts stopping for a mid day meal/snack in the rain, having that portable roof over my food is comforting. Sometimes the boys look at you inquisitively, while others have seen it before and are carrying their own.
Using a tarp? Open the umbrella and create a wind/rain block (make sure you stake it down!), or a privacy screen at the opening. And of course that wee early nature call it is nice not to don your entire rain suit only to bring it back in your shelter to moisten everything in the tarp or tent. I have never had to use it to prop up a tarp, nor would I try to. As far as being a sun shade device, I’ve not been in a situation where I needed that. I usually depend on my hat and clothing.
I still carry a full rain suit for those times when you just can’t hold the umbrella or the torrential downpour is driving horizontally. I have tried to a) tie it to my trekking pole and b) attach it to my pack. I will never tie it to the trekking pole again (too much trouble and an uncomfortable grip). I will likely attach it to my pack again, but more likely just to lay the pole over my shoulder with a mini-biner clipping its wrist cord to the shoulder strap. While it may be comical, it’s not fun chasing it across a field of fox-tails and spear grass if the wind catches it.