The objection to automating lead assignment is almost never that the rule is wrong. It is that when a lead ends up with the wrong agent three weeks later, nobody can reconstruct why.
Version the workflow
A workflow that is edited in place has no history. The run from last month is attributed to rules that no longer exist, and the answer to "why did it do that" becomes a guess. Every change should create a version, and every run should name the version that executed it.
Log the failures too
A step that was skipped because the contact had no email address should say so. Logging only successes produces an execution log that is technically accurate and practically useless.
Stop the loop before it starts
A workflow that updates a field, triggered by that field changing, will run until something stops it. That something should be the platform, recorded, rather than a message quota or an invoice.
Automation is only as trustworthy as the account it can give of itself afterwards.