Most working linguists do both: documents by day, assignments in person or by video when the diary calls.
One policy, both activities, in writing – that's the whole game for dual-practice linguists. Add the modern wording checks (MTPE sign-off, video interpreting, US clients), take the membership discount your professional body has already negotiated, and mirror your cover limit in your contracts' liability caps. Building an agency? You've outgrown freelancer policies – broker time.