Established Orgs often have Lead or Case Assignment Rules already set up. The Lead and Case object can each have one Assignment Rule active at a time. Whilst Plauti Assign works well alongside Lead and Case Assignment Rules, there are a few things you should consider when implementing Plauti Assign in conjunction with Assignment Rules. Below Lead Assignment Rules are used as an example, but this applies to Case Assignment Rules as well.

Native Assignment Rules run after Plauti Assign
When a record is created, Salesforce does things in a certain order. What is relevant here is that BEFORE triggers (such as the one employed by Plauti Assign) fire before the Lead or Case Assignment Rule. So if you have Plauti Assign rules and a Lead Assignment Rule that are not mutually exclusive, you will find that the assignments you expected from Plauti Assign are overridden by the Lead Assignment Rule. An important concept to understand is that if the lead does not match any of the Lead Assignment Rule Entries, the Lead Assignment Rule will assign the lead to the Default Lead Owner (set in Salesforce Setup > Feature Settings > Marketing > Lead Settings).
So the two things to consider:
- Don't have overlapping or duplicate criteria between Plauti Assign and the Lead or Case Assignment Rule.
- Always have a rule entry at the end where the Do Not Reassign Owner checkbox is ticked.
The other thing is that Web-to-Lead forms invoke the Lead Assignment Rule by default, so if there are no rules, it will assign the lead to the Default Lead Owner, overriding Plauti Assign. So if you use Web-to-Lead with Plauti Assign, you must always have a Lead Assignment Rule with an item that has the Do Not Reassign Owner checkbox ticked (that's rule entry 3 in the image above).
Furthermore, if your Leads are set to always 'Use Active Lead Assignment Rule' then you need to have that rule entry with Do Not Reassign Owner checked.
If you need to stop the Lead Assignment Rules from re-assigning leads that you have assigned in Plauti Assign, you need to have a rule entry like this (with Do Not Reassign Owner checked):

Assignment Rules for Queues
Plauti Assign doesn't let you assign to Queues by default, because Leads and Cases often go stale and forgotten in Queues. However, some Orgs have to use Queues for one reason or another. In that case it is recommended you use native Lead Assignment Rules to cater for any queue assignment needs you have.
In the image at the top of this page, the first rule entry matches when the Company is Acme. In this case, the company has a couple of Acme Specialists in a queue of that name. Alternatively, they could have a Plauti Assign Match Group for Acme Specialists where they would get the Leads assigned directly to the queue members in real time, with notifications, and with the ability to vary the distribution or cap their leads.
In another scenario you might have a Queue that you've created to catch any Leads that don't match on anything. For example rule entry 2 in the top image - that rule matches when the Use Plauti Assign field is NOMATCH. That will assign to a Lead Queue that you've set up for this purpose. Nevertheless, it is recommended to analyze what kinds of Leads these are, and instead create a Match Group that immediately assigns these Leads to exactly the right people.
See also Assign to a Queue if Plauti Assign doesn't assign the record.