When you need one. Okay, that's not much use.
What utilities are you going to provide? Utility stations I've seen contain a combination of steam, air, water and nitrogen in various combinations.
Steam is typically used by operations for freezing/thawing frozen or heavy hydrocarbons that have set up in piping. It's also used for helping to clean up spills in some cases and firefighting.
Water is used for cleaning.
Air is commonly used by maintenance for running tools. Operations also uses it for things like air movers.
Nitrogen is used for vessel purging.
Take a look at the equipment in your area, your list of utilites, hose lengths your company wants to use (several can be linked together but Operations won't be happy being told to run 20 hoses to reach an area) and lay out your utilities that way.