I install heavy duty tubes at home but carry standard for spares on the bike due to space.
The spare might take up less space, but if you actually use the spare, you still have to pack out the original HD tube, which takes up a lot of space. I used the HD tubes for a while, but like I said, I found no real benefit for general DS riding. I've ridden in Oklahoma, Arkansas, Missouri, Big Bend NP and SP, all over central and East Texas, Arizona, New Mexico, Utah, SW Colorado, Alabama, North Carolina, and Northern Mexico. A LOT of that has been in VERY rocky terrain on loaded down bikes. I've even done rocky and rooted single track riding. I don't think I've ever gotten a single flat on the front from riding, although I've had a few just from tires aging and the valve stem base leaking at the tube. I've had a few rear flats from punctures, but a HD tube would not have prevented any of those. I have NEVER had a pinch flat that was not tire tool induced
But again, I think tire pressure has a LOT to do with that. Running really low pressures with a regular tube may lead to pinch flats in cases where an HD tube might prevent one.
For what it is worth, I NEVER use SLIME in any tires
I have used it. It has never worked. It has ALWAYS made a HUGE mess in every single case!! I find it much easier to leave it out and just deal with a flat if I get one. Some folks will swear by it though. I think that might be more like the deer whistle effect though, they've never gotten a flat while using it, so it must work
Some folks use Ride-On. That is actually different than SLIME. It may work. I have never tried it.