I think for any in-depth discussion regarding belts, one would need to talk specifics. Different lifts and even different variations of each lift will effect usage in various ways:
Raw Squats: Specificity will of course mean you'll be doing these belt-less. However in terms of assistance a belt to increase the amount of weight you can use is a useful way to overload the surrounding areas.
Equipped Squats: Specificity dictates you would use the belt as the weight get's heavier. You can use the belt in numerous ways, by having it lower and pushing against it with your abs. Or having it higher up can work as well, especially with lifters who have to bend over a lot in the Squat and will have issues with the belt hitting the thighs on the way down.
A decent assistance will be to go beltless to increase strength in the midsection muscles.
Conventional: Many decent conventional pullers don't use a belt, or rather use a belt which is thinner. KK is the notable example of this. Depending on bodytype and particular strengths of the lifter the heavily bent over position may mean that the belt hinders rather than helps.
Sumo: Almost always the belt will help here, due to the more upright position and consistently arched/flat back. There shouldn't be issues reaching the bar, either equipped or raw.
This wide spread of variations, strengths, weaknesses, bodytype and intended training effect all play a role in whether using the belt is useful or not and account for the many arguments for & against on the forums. As always the answer lies in the individuals situation.