LOC is a poor way to measure progress, but it's not a bad sanity check on time estimates for a proposed project. Most experienced programmers have some points of reference where they know the approximate LOC count, and can make a rough functionality/complexity analogy to a proposal. If the proposal is less time than the team could possibly generate a comparable amount of tested code at 10-100 lines/day (wherever your team is in that range), then you should probably revisit the estimate.
Apply a few of these kinds of comparisons using different metrics, and you may be able to improve your estimates.
Apply a few of these kinds of comparisons using different metrics, and you may be able to improve your estimates.