You will get more and smaller curves. Nothing will be wrong though, there will just be many little pieces. Other systems do not follow the rules completely but to some tolerances. Use allow open, and allow self intersect to relax these requirements. If the trim curves are really crummy, the result will look crummy, but it is the fault of what is written in the file.
Relaxed mode is the recommended option.
If you do not use the relaxed mode, the log file will indicate when an occurrence of open or self intersection occurs, along with directory entry into the file. The tolerance is the allowed variation between the original geometry and the bspline. The larger the tolerance, the simpler the resulting bsplines will be. It reads only the directory section and reports on its findings. We also inform you when an entity is defined as a 2D parametric entity.