The assignment rules are basically used in order to do the lead generation of groups. The assignment rules will allow the manual finding of leads that may be taken from various websites online or from various sources. There are times when companies use import wizards in order to get leads and there is nothing wrong with that because companies would need to know who may become interested in their products.
The more leads that they get, the better their business might turn out to be especially with proper marketing and advertising involved. Take note that case assignment rules are not time-based.
No, case assignment rules run immediately, usually on case creation, although you can call them later also. There is no time component to assignment rules