Weighting duties in a job description?

MrCreosote

What do you think of assigning percentages to the essential duties in a job description? The idea is that reviews would be weighted, based on those percentages.

For example, for a teller:
50% - Receive and process customer financial transactions.
25% - Welcome customers and provide info
10% - Post transactions to accounts
10% - Balance cash drawer
5% - Other duties as assigned

My concern is that someone might argue that a duty that is only worth 5% or 10% is not really "essential." I'd like to know if this is a common practice and your opinions or experience.

And thanks to those who responded to my last jd question.

Don D

But, a duty that is performed only 1% of the time could be the most critically essential of all. For example, the branch VP or Head Teller of a bank branch might have a very critical duty to open the vault, shut off alarm systems and secure the cash at precisely 8:40 a.m. day after day with no margin for error. Or a school principal might have a 1% duty to alert all staff and students of certain emergency things using the PA system, something that carries a large consequence of error, but which makes up only a minimal part of the day or week.

MrCreosote

The percentages are based on the importance of the duty rather than the time spent performing it. In general terms, 50% of the annual merit increase might be based on the duty weighted at 50%, 10% of the merit increase based on the duty weighted at 10%, etc.