Traditionally, a subpoena requires a witness to appear on a specific date, time, and place, usually at a courthouse or a lawyer’s office which may be inconvenient to the home or workplace of the witness.
However, with most, if not all proceedings now being virtual, subpoenas in these days of COVID usually provide the witness with a Zoom link that the witness can access on the date and time called for by the subpoena allowing the witness to appear and testify from the comfort of their home or office. This eliminates the need for a witness to travel downtown by train or fight traffic and park in the Loop which for many is a stressful experience not to mention expensive.
It will not surprise me if this practice remains in place in some manner once the Pandemic is behind us.
For more information on how subpoenas work, you can watch these FAQ videos from Partner Ken Hoffman.