I'll admit I'm not as fastidious with my engagement letters as I should be, partly because of this I'm thinking of moving to annual engagement letters.
I think such a move would have a few benefits
It makes me review and update the engagement letters for changes, i.e. new services, MTD, AE, GDPR etc.
It reinforces to the client the work we have agreed to carry out, and any work which would cost extra. As well as putting a clear end date to the work we have agreed to carry out. Which would no doubt help in a disagreement with the client.
I think it would also help when making changes i.e. I have been trying to get all clients on gocardless, I'd make this mandatory on the next signup.
Finally, it provides a good opportunity to review fees.
The only potential downside I can see is it may make it easier for client to leave :D
Any extra admin work would be small and with eSigning it is quick and convenient for the client.
Go on, tell me I'm crazy.