Let us say if I specify two comp A and B.
For A
Priority 1
Strategy 2 ( 100 %)
Usage prob. 30
For B
Priority 2
Strategy 2 ( 100 %)
Usage prob. 70
Do I need to maintain usage probability?
How system will behave, will it ignore usage probability?
Answer:
Usage probability is for MRP run.
Priority is the order in which stock is checked in order to reserve.
If either 100% of A or 100% of B can fulfill the demand then it will pick that component based on priority (A first, B second).
Let us make it a little bit more detailed.
Component A
Priority 1
Strategy 2 ( 100 %)
Usage prob. 30
Qty reqd in BOM : 20 EA
Component B
Priority 2
Strategy 2 ( 100 %)
Usage prob. 70
Qty reqd in BOM : 10 EA
If Available stock
A: 20
B: 10
Component A is picked to make reservation.
If Available stock
A: 4
B: 6
(After MRP run)
pur req for A: 2 EA and
pur req for B: 1 EA
If Available stock
A: 0
B: 0
(After MRP run)
pur req for A: 6 EA and
pur req for B: 7 EA
If either 100% of A or 100% of B cannot fulfill the requirement then MRP run will look at the usage probability and generate purchase orders based on the probability and available stock.
But you want to purchase either component A or component B (according your requirement where you want to make one of them primary), it makes little sense to set one at 30% and other 70% so you set that component usage probability for primary as 100% and rest of the components in the group 0 so that pur reqs are generated only for the primary.
Example, you always want the system to look for A if it's in stock and can fulfill demand but you always want to purchase B first, so you set priority 1 for A and probability 0 and usage probability 100 and priority 2 for B.
