I have huge line and polygon shapefiles that I want to edit with some geoprocessing tasks (clip, buffer, erase,...). Altough my computer is not that slow, I am annoyed of waiting up to 15 hours for one of these tasks. Some people say that importing the shapefiles in a File Geodatabase will help. Are there any further hints? Is there any difference whether I perform such ArcGIS for Desktop tasks through the ArcCatalog or ArcMap applications?
ESRI has a blog post - aptly titled Dicing Godzillas - about processing feature classes with large amounts of vertices. It discusses the Dice tool, which splits up a shapefile's features into smaller features with less vertices.
You won't find much of a difference (if any) running in ArcCatalog vs. ArcMap. However, you might find some improvement by running it entirely outside of either by using Python. If your data would benefit from being split up, you could use Python for multiprocessing, which is discussed here.
Still another option (that can be leveraged via scripting or ArcMap) would be to use the in_memory workspace. This doesn't always work for really large files as you'll get memory overflow errors, but it might be worth a shot if you will be processing this dataset multiple times.
Depending on your data, you can try combining all of the above to see what works best for your situation and data.
Other than that, running it overnight is always an option. Good luck!
Edit @SeaJunk's comment: If you are running ArcMap 10.1 SP1 or above, definitely take a look at Background Geoprocessing. Great tip!
Any time you are looking at a heavy process consider scripting it out with python.
By scripting you do not have to worry about ArcMap or Catalog having to load all of the other overhead (such as the UI) that you do not need while running your process. If you have multiple steps, the script can launch right in to those with out waiting for you to click the button (you don't want to be there just to click the button at 1 am to get the next step going). Finally, by scripting it you make it easier to rerun the entire process in the future for any reason.
Yes, these last two can also be accomplished with a model, but you have to deal with the extra overhead of ArcGIS Desktop, you also lose out on better error handling and the flexibility that Python has to offer.
As for the file format, I recommend you get your data in to one of the geodatabase formats. The geodatabases seem to be less prone to file corruption than shape files. Up to 1GB you can use either the Personal Geodatabase (.mdb) or File Geodatabase (.gdb). Bigger than that the .mdb geodatabase starts to get flaky due to the design limitations of MS Access.
Another thing that will help significantly is storing your shapefiles (and your output files) on the computer's SSD, though it sounds from your comment like you're already doing that. Converting your (huge) shapefiles to file geodatabase feature classes will definitely help too, but not nearly as much as splitting your shapefiles into smaller chunks and processing them separately as Paul suggests.
I am not sure if this will help you or not, but I have realized that if you have a very big polyline shapefile and you want to for example reshape it, it would be much more faster if you split it into smaller parts. To do this you may use a sort of paneling or a mesh polygon to split the polylines. This is going to reduce the process time considerably and in the end you have the option of merging them together.