"you can cover only small department fitted in one room" - this is the most important part to remember when someone comes in waving their ISO certification and has beautiful badge on their website. You can certify your secretary, her cat and her desk in whatever fancy ISO certification you want. Funnily enough it does not really cost that much, there are consulting companies that gladly organize this for a few thousand dollars. This works like this for all ISO certifications.
Another thing, introduction of ISO in the company means only that there is some process to do X within the company. This process can be totally nuts and useless, but ISO certification holds as the process is there.
In general ISO makes a lot of sense for production line environment (like cars production, etc.) - the process is everything there, having someone to review this process is important and valuable, many other ISO certs are just marketing tool that does not really tell much without going into details what processes are covered by ISO.