To further clarify, obviously if your reptile is ingesting a lot of substrate that puts them at risk for impaction. However, this shouldnt be happening if you're not feeding directly on their substrate (in other words, using a food dish or tong feeding), and they're otherwise healthy. Any small amounts of substrate ingested when burrowing or that may come in contact with food should have no issue being passed by the reptile... assuming it's an appropriate substrate. You don't want something that clumps when it gets wet, for example.

Temperatures that are high enough for the animal are important because this keeps their metabolism where it should be and allows them to digest and pass what they've consumed properly. This prevents anything, food or substrate, from sitting in their digestive tract to accumulate.

The majority of the reptiles that suffer impaction in captivity are impacted because they have either ingested something extremely difficult to pass (such as certain kinds of sand, repti carpet or shelf liner, large chunks of wood or rock, clumping substrate, large wads of paper towel, etc) or they weren't provided with basking temperatures warm enough to facilitate normal digestion leading to the buildup of food and anything else in their gut.