Limiting search to few shards by providing routing IDs

[vivek7mehta (vivek)]

I am not sure if this question is already asked, I tried to search and couldn't find what I was looking for.
I am using routing to reduce my search impact. I am providing routing IDs while indexing (e.g. user1, user2, user3....).
So if I want to search documents I can search it as:

GET my_index/_search?routing=user1,user2
{
 "query": {
  "match": {
   "title": "document"
   }
  }
}

Now my questions are:

1. how can I search on all routing IDs except specific set of routing IDs? (e.g. I want to search on all IDs except user1, user2 and user3) ?
2. If I use _routing field in the query will it use routing at all?

GET my_index/_search
{
 "query": {
  "bool": {
   "must_not": [
    {
     "terms": {
      "_routing": [
        "user1",
        "user2",
        "user3"
       ]
      }
    }
   ],
   "must": [
    {
     "match": {
      "title": "document"
      }
    }
   ]
  }
 }
}

[Christian_Dahlqvist]

The main benefit of routing is that you can hit a single shard instead of all. If you are likely to hit the majority of all shards, just query without routing.