I have a hard time understanding some definitions and usage of quite in English Grammar Today (via Cambridge Dictionaries Online). The explanation is as follows:
Quite a bit, quite a few, quite a lot
We often use quite with a bit, a few and a lot to refer to large amounts and quantities:
You should ask Mez for some advice. He knows quite a bit about gardening.
(I don't know if he knows a lot or a little about gardening, because of a bit is used here.)
A: We bought quite a lot of new furniture, didn’t we?
B: Yeah, quite a bit.
(Do quite a lot and quite a bit suggest the same meaning? Does quite a bit mean "very little"?)
There were quite a few of us at the meeting.
(What does quite a few mean? Does it mean "very little"?)
We also use quite a bit and quite a lot to mean ‘often’:
Do you come here quite a bit?
(Do quite a bit, quite a lot, and quit a few have the same meaning in this context? If Not, why?)
I used to go sailing quite a lot.
(Can we use quite a bit or quite a few here without changing the meaning of this sentence?)
Quite + a lot /a bit + comparatives
We often use quite a lot and quite a bit with a comparative adjective or adverb to mean ‘much’:
We went to Italy when I was quite a bit younger.
(Can we use quite a lot or quite a few here without changing the meaning of the sentence?)
The new truck is quite a lot heavier than the old model.
(Can we use quite a bit and quite a few here without changing the meaning of sentence?)