Annual mortgage payments, terrible idea?

I've always paid for things annually over monthly, so just thinking out loud as rates change.

Within the 10% I can overpay, I could dump the years mortgage payments and let that overpayment be consumed each month untill doing the same for the duration of the fixed term.

It seems that's perfectly allowed in the terms, but what would that do to the daily interest? Will the lender hate this, not seeing a monthly amount?

The main catch I see is that money is gone, if anything happens I need more savings. But I feel pension contributions are the same.

Does anyone do this? I've left out the idea of additional overpayments to simplify the question, you already have excellent 'vs savings' advice.