Right now, if you create a new lookup, it very helpfully offers to let you use the default relation or the joins between existing lookups in that table. This feature is incredibly convenient; I use it all the time.
There are many situations in which the a lookup must use top with a sorting, or must use a condition in order to work properly. It's currently possible to clone an existing lookup and change its lookup field, but this method is clunky at best.
If you were able to choose to use the aggregation, sorting, and conditions from an existing lookup when creating multiple lookups in addition to the existing functionality of copying joins, it would greatly speed the creation of complex lookups.