When to say "i" before a Welsh verb

[lynn-thomas]

I notice that sometimes there is an “i” before a verb; is there any rule about this?

[JohnYoung]

There’s a helpful topic on this. I’ll try to find it.

[JohnYoung]

I think this is the best thread -

When to use and when not to use 'i ' as a preposition before a verbnoun

In the sentence "Would you be willing to bring something to drink with you?’ (ch. 10 level 2 N) ‘i’ is used before ‘yfed’. In the sentence “Would you be willing to wait for him?” the ‘i’ doesn’t appear before the verbnoun ‘aros’. I’m puzzled why it is used before one verbnoun and not the other. Is it just an optional thing?