I think the soft cap is very necessary for an ICO project because the soft cap is a sign of their minimum fund to run the project. thus can be more convincing to investors in supporting the project.
but actually the guarantee regarding softcap will make it a road or not it is not determined by it because it is funding to run while whether it is successful or not is not a determination
But stopping at softcap may delay the execution of the project because they have to start cutting down on all their budget using hardcap and removing most part that they initially thought was necessary for the project or the ones that will facilitate the project but I know that a very serious minded developer with a sound project will be able to work with softcap and push the project hard till it see the light of the day.
I also suspect that most developers that have stopped at softcap end up still investing the fund in some projects they believe to help them double it to the original price quoted for hardcap, probably reasons why we see lots of delayed projects.