Tags are intended as labels to group or classify queue items, eg male/female, loan account/credit card account/savings account. They aren't designed to carry unique values like customer IDs, phone numbers etc, and filtering on tags can result on DB performance issues when there are a high number of unique tags. What is a high number is hard to say as there are lots of unknown dependencies such as table sizes, solution design, infrastructure etc.
If you contact Support they will be able to advise you on housekeeping and may provide you with clean up scripts.
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John Carter
Professional Services
Blue Prism
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