Steam should be treated just like any other application installed on a business computer. Ask yourself if it is needed to perform your job correctly.
When your computer has more software install, it has more areas it can be attacked.
Steam may not have a vulnerability now, but they may accidental release an update that will have a vulnerability in it.
There may be 0-day vulnerabilities in steam that are not yet released to the public.
A hacker may be able to get into the Steam code and make some modifications that will allow a backdoor with all updated Steam client.
With this in mind, not having Steam installed will prevent any of those vulnerabilities.
Furthermore, good system administrators will remove any unnecessary programs or services for servers or workstations.
Go though a thought process like the following:
- Does my windows 7 machine need Bluetooth?
- Is it enable or enabled by default?
- If my system is compromised, is my data still safe?
- How much money should I invest in preventing an intrusion?
Of course if you develop the steam software or develop software that uses steam, you probably should have it.