We know that innovation often arises from an odd or unexpected coming together of people with disparate skills, different attitudes, different knowledge sets and perhaps different attitudes. There are even innovation approaches and techniques that aim to simulate (or stimulate) these 'comings together' amongst individuals.
Yet over the last few years we have allowed workers to choose to work from home where such comings together are impossible.
The water cooler, the kettle, the snack machine are places where people gather (informally, yes and for a short time) but brief interchanges of information, progress reports, ideas, even complaints can get others thinking.
When would you not encourage (or even insist on) people coming back to the office to make these interchanges possible once more. It may not give you immediate revolutionary innovation but it almost certainly does no harm - and it does help employees engage with their colleagues and with the organisation.
You might even think of new ways of creating interaction and idea-generation and use this as an attraction to entice people back to the office.