In the mishnah brura there is a clear hakpodah not to have anything between a mispalel and the wall during shmoneh esray, unless its something thats kovuah. Why is it that many people davening shmoneh esray go out of their way to place a chair in front of them, in clear violation of above halachah?
Answer:
The reason some do this is that the chair helps them in their tefillah – they place their hands or their siddur on the chair, and it therefore serves them much as a shtender does.
The halachah of not having anything interrupting between the person and the wall does not apply to items that are used as part of the prayer service.
Best wishes.
