gerund

For above, 'which gives you considerable saving', saving is a noun, not a verb. So it's actually not one of the use of gerund.

And second, about the 'shopping': After you use 'when', 'of', 'by', 'in', 'as' or something like that, you need to use gerund. The reason is simple, because after those words you won't have a subject. You can't just use a verb to instead of a subject, such as 'I jump off as I slip', you can't change it into 'I jump off as slip'. You can see, the sentense's structure isn't correct, nor can it gives a correct message to others. After those constructive words (or, by, in, as, with, when,...), you need to use a noun or noun phrases followed by. Changing words to gerund (that means +ing) is one of the method to maintain correct sentense's structure.


*P.S. There's some other situation you need to use gerund. As when you have two words in one sentense, you need to change the latter one into a gerund. That means add "ing".

e.g. 'I go swim' is wrong. You can change it into 'I go to swim', OR
USE A GERUND : 'I go swimming'.

thanks both of yr great effort on my question , especially, 001

shopping points plan - "shopping" here is used as noun compounds. The gerund here carries the main stress.

but "saving" - I don't see it as gerund, to me it is a noun.

Gerund can be used:
1. as subject of a sentence - Reading English is easier than speaking it.
2. as complement of a verb - My hobby is reading.
3. after preposition: I have difficulty in finding a parking place.
4. after certain verbs: I love dancing. I like skiing.
5. in noun compounds : shopping points plan