Tasks\\bugs in the project management system?

progress for atomic jobs — a fiction, for aggregate is needed only for reporting and is only necessary for any thread glubokovodnykh splits that do not cover eyes. Or if a lot of them. In General, progress is addressing some external to the workflow problem.
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the priority for tasks is needed only at the stage of planning/replanning, although probably important for the dynamic methodologies. But in General, minor — is more important to have dependencies.
For bugs we need not the priority and severity, although whatever you call it... but it is rather in the direction of the display with the SLA tracking.

Priorities are needed, but what is a very interesting question.
Example — there are two projects to do by any one. If one of them has a higher priority (for example platform dependent debt payments/RFP), the question of what to do will not.
Progress is also needed in a similar situation if you have a project with 99% — it is better to deal with it, not sprayed on it and another which has only 5% ready.

We do not use any priority or progress. We have one field — the urgency. Moreover, it is set in the form of numbers from minus infinity to plus infinity — thus, at any given time, you can create a more urgent task