Currently the IF conditions in Rules & Processes require a lot of condition duplication in order to evaluate every combination of conditions independently. It's inefficient from a config standpoint. But more importantly, it wastes a lot of server resources in the way of processing cycles, memory, etc.
Nested If conditions would increase configuration efficiency and also run much more efficiently meaning faster response times and support for more concurrent users.
Example:
Without Nested If's, every combination of conditions has to be checked independently.
IF Account.Active = True AND Account.Balance = 0 THEN
Do Action1
ELSE IF Account.Active = True AND Account.Balance > 0 THEN
Do Action2
ELSE IF Account.Active = True AND Account.Balance < 0 THEN
Do Action3
With Nest If's, if an Account is Active, the evaluation of the nested conditions continues. If an Account is not Active, the rule evaluation process stops after the first IF.
IF Account.Active = True THEN
IF Account.Balance = 0 THEN
Do Action1
ELSE IF Account.Balance > 0 THEN
Do Action2
ELSE IF Account.Balance < 0 THEN
Do Action3