Please consider the following sentences -

1. There is no point (in) discussing this here.
2. Do you see any point (in) filling out the forms?
3. I don't see the point of repeating the entire process.
4. What is the use of filling up the forms?
5. There is no use sticking to this old policy.
You see in some sentences prepositions are optional, but in other sentences they are not. Where prepositions are optional I have placed them in brackets.

My question is -

Why in some sentences omitting prepositions are optional, and in some they are not? Please give some grammatical explanation. I am asking because I want to learn it, so that when I try to write some other sentences I don't make any mistakes.
Thanking you in advance.