I seem to remember hearing in one of my lectures that children engage for longer at tables where they can stand at an activity rather than sit at an activity. This would make sense because young children engage with activities in a physical way.
A lack of chairs also means that as many children who want to can engage at an activity.
But the logistics of leaving the chairs away from the tables can be tricky, especially if tables are used for a variety of activities.
Chairs can also help manage the number of children at an activity - if I only have enough material for (say) 5 children to play at once then I put five chairs out and ask other children to wait until a chair is free to play at that table.
What do you think? Chairs or no chairs? A mix of both?