Some people advocate assigning priorities to tasks while others say that’s not necessary. I prefer to.
I assign priorities to tasks so that no matter where I am I can quickly glance at my list and know which things I think I need to do that day. If I am using a GTD-type system and I am working by context (say @phone), and I have assigned a number or even a letter and a number to that task, I can easily see which calls to make first because today I have to make sure that I get those numbered tasks done today. And, that is important when I only have a limited amount of time or energy to spend working within that context. If there are no numbered tasks for a particular context, I know none of these are urgent and I can work on them in no particular order.
Using GTD and a numbering system is an example of combining systems, such as Julie Morgenstern or Stephen Covey‘s, into hybrid beings that suit our own situation and or own productivity planning needs. So, if you want to and if it helps you, go ahead and assign that number or number and letter.