for example to be able to lock a geometry such as a surface patch adjacent to a crease edge so that it is not deformed by the crease being added.
SubDs edges affect their immediate adjacent edges- that's how they create smooth surfaces.
Your best bet would be to insert a loop next to the edge you want to crease, but in the command panel, check Preserve Shape- if it works (and sometimes it can't), that gives you an extra edge buffer zone and hopefully doesn't deform the part that already looks like you want it too.
Best practice is to set your creased edges during the modelling process, not after
hope that helps,