Tables and desks may cause some electromagnetic fields that are very difficult to remove.
First there are desks with electric wires inside, so even if the table is made entirely of plastic or wood there are the electric and magnetic fields created by such cables.
Another problem is caused by metal frames, bars, plates and other large structures.
For example consider a table made almost entirely of steel or other metal. If there is an electric cable near a leg of the table, and the cable has not a perfect electric shield, when the cable is attached to the electric socket the whole table is surrounded by an alternate electric field. If the electric cable instead passed near a leg of a completely wooden table the alternate electric field on the table would be hundreds of times lower.
Often there are tables and desks that apparently are made of wood but they have some hidden metal structure. This tables or desks are better than the metal ones, but they have still a much bigger electric field.
To avoid this harmful electric field a completely wooden desk is preferred, without any large metal parts inside the legs, or under the top plane. The table can also be made entirely of some kind of plastic.