The expressions that is to say and at least can be used to back down from an unpleasant or negative remark you just made.

I am not going to talk to her again. Well, that’s to say, not unless she apologizes to me.

I’m afraid is used to introduce a polite refusal or bad news.

‘Could you please lend me a pound?’ ‘I’m afraid I can’t.’
‘Could I talk to Annie?’ ‘I’m afraid she is not in at the moment.’

I suppose can be used to enquire politely about something.

I suppose you are coming with us? (A polite way of asking: ‘Are you coming with us?’)

I suppose can also be used to express unwilling agreement.

‘Could you lend me a pound?’ ‘I suppose so.’

Or rather is used to correct oneself.

I’m going to London in May – or rather early June.
Let’s meet next Monday – or rather Tuesday.

I mean can be used in the same way.

I’m leaving on Monday – I mean Tuesday.

Gaining time

The expressions let me see, let’s see, I mean, kind of, sort of are also used when the speaker wants time to think.

‘How much are you asking for this?’ ‘Well, let me see…’