It depends on the situation. For example, if a customer asks a service from you and if you do a shoddy job, it's not very good. What you want to avoid is time wasting or idiosyncratic perfectionism. So categorize what you do into the following 2 groups and use the respective guidelines to avoid time wasting perfectionism.
- Providing a service to another: Have you delivered what's promised with the standards agreed upon? If yes, stop and move on to the next.
- Your personal duties and goals: Is the objective beneficial? Have you done enough to achieve the said beneficial objective? If yes, stop and move on to the next.
Once you stop, if unreasonable thoughts keep coming to make you want to waste time on something, be mindful of them until they go away. Ex: wanting.... wanting.... wanting....