Grid gap is great when your have a website that would support both "LTR" and "RTL" directions. For example if you'd use margins only, margin-left may become foolish in RTL, but useful in LTR.
So you definitely should be using Grid gap as a replacement for margins.
The actual good use for margins is only vertical margin.
Anyway, if you have a website you know for sure would only support one direction, either "LTR" or "RTL", you can use margins instead of Grid.
You just need to prevent the last element in a row to have an ignorant margin by using the selector ":not(:last-child)".
Grid gap is great when your have a website that would support both "LTR" and "RTL" directions. For example if you'd use margins only, margin-left may become foolish in RTL, but useful in LTR.
So you definitely should be using Grid gap as a replacement for margins.
The actual good use for margins is only vertical margin.
Anyway, if you have a website you know for sure would only support one direction, either "LTR" or "RTL", you can use margins instead of Grid.
You just need to prevent the last element in a row to have an ignorant margin by using the selector ":not(:last-child)".
For those bi directional sites you can use CSS Logical Properties in that case for
margin-leftit would bemargin-inline-start