Let me give an example of how to rewrite part of the copyleft concepts as pure permission rather then term and conditions.

"I here grant permission to distribute source code of the unmodified complete work"

"I also grant permission to distribute a binary version together with the corresponding preferred source code of the unmodified complete work"

"I also grant permission to distribute a compilation of a modified version of the source code with the source code of all dynamic linked software that it depends on"

Of course, to match a license like GPL you would need to make precise wording to get the permission to mean exactly one and only exactly one permitted action (lawyers, interpretation and loopholes), but they are just plain permissions. You can use one, two, or ignore any number of them and mix and match. Since they are isolated permission they hold no state and there is no "I agree to all terms".

This is also the main argument behind the concept of software license not being contracts. A contract goes beyond permissions and binds two parties together in one document, while permissions just exist regardless if anyone accepts it.

You are bound mostly when you distribute GPL covered works or derivative works. The licence is a-priori unconcerned whether such derivative work involve IPC or dynamic linking or anything else. There is no trivial relationship between the technical kind of SW interaction and if it constitutes a derivative work or not. Sometimes projects clarify their interpretation, e.g. Linux telling (with much reason!) that merely using standard syscalls does not per-se constitute a derivative work - (and note that this is a quite stronger form of interaction than most IPC, however this does not intrinsically prevents some IPC usages to be considered as derivative, maybe especially if such IPC are added after the fact in a vain attempt to circumvent the GPL with a meaningless technical trick)

Any time that you want to use the software and you're not the copyright owner. The terms of the GPL grant you permission to use it under some circumstances that you wouldn't have otherwise.

It is true that sometimes it is not clear when you are satisfying the conditions in the GPL that allow you to use the software, since there is no case law. But the constraints that forbid you to use the code all come from copyright law, not the GPL itself.