To add my .2$ in the discussion :-) It's true that the question of performance is something very tricky to get it right.
One thing is also true, is that too much indexes is not a good idea either, first it takes too much space in the database.
Second, you will slow down the load as pankaj said, but also it will give problems to archive document in parallel for the same application group.
(we have found recently by one of our customer, that with 1 index, he can do parallel archiving in 1 AG, and with lots of index, everything is archive sequentially).
The idea of indexing field is also tricky, because if you have a field that is really unique (like a doc id)... and you index it, then you loose the benefit of using index.
If your date for the segment is also an index, and you are using 1 document per day... then the fact that you have an index is not really useful too.
Best would be to have as few indexes as possible, and to select the best candidat for it (like customerNo, Date (if several dates per day), ...).
Sincerely yours,
Alessandro