Line profile analysis of X-ray diffraction (XRD) peaks is a widely used technique to characterize particle size and strain distributions in nanocrystalline samples. The accuracy and precision of the traditional methods were tested using silicon-on-insulator (SOI) thin films. By accounting for instrumental broadening, these analyses show an accuracy of ±1 nm in determining film thickness, while the precision is 2 orders of magnitude less. The same methods are also applied to strained SOI films, where we definitively demonstrate that line profile analyses are sensitive to strain distributions and not uniform strains. Furthermore, the traditional analyses are highly quantitative only when the main assumptions of the theory are met. The results of these studies were used for two different applications. Through rigorous modeling, we simulate the two-dimensional diffraction profile of an SOI sample obtained from a coherent, focused, nanometer-sized X-ray beam. The results of the simulations are in excellent agreement with experimental data obtained from such a source. In the second application, we utilize line profile analysis to characterize the kinetics of anomalous coarsening in copper thin films. Both of these applications were made possible since the initial studies conclusively showed that SOI films are ideal structures for testing XRD-based techniques and analyses.