Related: Is it appropriate to use irasshaimase when welcoming someone to a private office?
In the related question, the target is "someone", which brings me to the conclusion that OP there means "if anyone other than people working in the same office arrives, should いらっしゃいませ be used?".
For example, when clients of a software engineering firm you're working for visit your office, is it customary to say いらっしゃいませ since they are customers, or is いらっしゃいませ usually just said in a service-oriented environment (such as restaurants, hotels, and shops)?
Context: We have a Japanese HR Officer who happened to be in the same room as us when the clients arrived and she greeted with いらっしゃいませ, which perplexed me a bit because I thought it was only used for restaurants and whatnot.