WHY DO WE USE ASSIGNMENT RULE , DATA LOOKUP

[abdullahkhan852]

@Dr Atul G- LNG @Sandeep Rajput1 @Mark Manders @Ravi Gaurav  
If we have client script to set value for any field or assign value .
Why do we use assignment rule , data lookup,etc

where does it work ?client or server side?
whats the difference between assignment rule , data lookup and data lookup definition , client script.

[Dr Atul G- LNG]

Hi @abdullahkhan852 

If we have a client script to set value for any field or assign value.
Why do we use assignment rule, data lookup, etc

Atul: Assignment rules are like OOTB and direct way, We use the Assignment rule when we have a set of values like cat/ sub cat and 2 more fields and then directly add the group.

Data lookup: As the name indicates, when we need to set some value based on some other values, by look up.

where does it work ?client or server side?
What's the difference between the assignment rule, data lookup and data lookup definition, and client script?

[Dr Atul G- LNG · Accepted solution]

Data lookup definition: It is like the base, where we define the table schema and set the source table. 

[Mark Manders]

Please don't tag people in your question! It's very annoying and won't help you in getting the answer any faster.