Since nobody will make the software I want I often have to choose between creating a task and creating a calendar appointment. Sometimes I do both, but mostly I do one or the other.
If it's a task I really need to get done (A) I schedule it on my calendar. I don't create a task. When I schedule it I add a note on what I want to do and what the next steps are (if any). I schedule the time I need to do the work. Sometimes there are some related tasks, but I try not to get fancy.
B Tasks are things I want to do. Sometimes I need to do them, but I may not have any capacity to schedule them. I put B tasks in my task/todo software and I usually assign them a target date based on their size and my predicted capacity. If they get more urgent I make them A tasks and schedule them (so in this case I have both a task and appointment, but it started as a task).
C Tasks are often ideas or future projects. Sometimes they're important, but can't be scheduled (too big, too expensive, etc). C tasks are a "backlog" of work. Periodically I purge them if they don't get done, but they mostly sit quietly in the queue, not bothering anyone. A C task can be promoted to a B task -- and it might even get a date. Or, if time/money arrives, they go straight to A.