If rates like tree ring growth or ice sheet buildups or erosion remain the same, this would be helpful in assigning dates to features. For example, if the amount of dirt in the Colorado River was measured at the mouth of the Grand Canyon to determine a volume for one year, and assuming you know how much volume is missing in the Canyon, you would be able to calculate how many years the Canyon has been forming. This model is critical in all age-dating schemes for the theory of evolution.
However, historically this model, also known as “gradualism,” arose in the 19th Century very much as an alternative to the Biblical record. Scientifically it was raised as an opposition to “catastrophism,” which is the belief that much of the geologic features of the earth can better be explained as having been formed via catastrophic events, like the Flood of Genesis. Uniformitarianism allows for much greater time in the formation of those features.
As was mentioned above, this model is used in dating tree rings, which assumes the rings are not growth spurts so much as annual rings and thus usable for dating. The same is true of ice packs, with freezing/refreezing sheets assumed to represent yearly events. It is the same with radiometric dating of rocks, where it is assumed that decay rates remain the same.
This way of relating to earth’s history might be being referred to prophetically in II Peter 3:3,4: “Scoffers will come in the last days, walking according to their own lusts, and saying, ‘Where is the promise of His coming? For since the fathers fell asleep, all things continue as they were from the beginning of creation.” That is, “No great event, no catastrophe has ever happened like that before. Things just go on and on like they are going on today!”