Customer Account numbering - skipping values in a sequence while using automatic numbering

Hello all - I am looking for pros/cons for the following scenario: a comapny tends to buy/merge with several other companies and then migrates their existing accounts into the main Oracle instance. Do you migrate them and use next available acct# sequence or do you set a sequence to represent the account you migrated and then reset your automatic numbering each time you migrate accounts from another company?

Example:

Current business in main instance: account_number sequence would create acct#100000 as next value

Want to create in a batch 1000 new accounts due to merger with company and need to migrate their data into main instance. What would be the pros/cons of creating the new acc#'s at lets say 500000 as a batch and not changing the next_val in the sequence so that a newly created account via the main instance UI would create acct#100000. Would the applications have a problem? What about the next company merger.....need to create another 1000 accounts in a batch but lets start at 600000....but new accounts via the UI are still using the next_val of the oracle sequence.