In simplest terms, it groups an Item's demand, within a defined time period, onto a single supply suggestion.
If I have 5 orders for an Item in a given week, and the total sales is 20 Units, the Lot-for-Lot policy can give me a suggestion to make/purchase 20 units so that they are all available on the first date of demand within the period (in this case Monday).
Lot-for-Lot is so much more than that. I find it to be the most flexible reordering policy because of all the ways you can modify the calculation. Adding Safety Stock to simulate a stock policy, adding min qty to simulate reorder quantity, adding order multiples to ensure you get bulk discounting. The best part is you can do all of those things at the same time, so you can get very specific with how the system makes its suggestions.
All that being said, it works best when you have known demand and time to replenish your inventory.
Hope this helps.
