It’s a really old fashioned way of thinking that you need to see someone sitting at a desk to know that they are working, when in fact that has no correlation to how productive they are being. The answer to this question is so completely simple: are they delivering results? Are they getting their work done?
At the end of the day, that’s all that matters. Whether they are sitting next to you in an office or working from the other side of the world, the metrics to measure that are exactly the same.