Why would you put Identity Increment other than 1 in SQL?
I have used identity increment other than one, especially in MERGE REPLICATION in different regions.

E.g. We have Publisher in NY and Subscriber in LD involved in Merge replication.

We set Publisher's Identity increment to ODD and LD server's identity increment to EVEN. This way you dont get conflicts where MERGE agent runs and tries to merge the changes.

I have talked here with a script that helps determine identity.