Beyond labor efficiencies, the determining factors in deciding to implement a WMS tend to be more often associated with the need to do something to service your customers that your current system does not support (or does not support well) such as first-in-first-out, cross-docking, automated pick replenishment, wave picking, lot tracking, yard management, automated data collection, automated material handling equipment, etc. 
Setup 
The setup requirements of WMS can be extensive. The characteristics of each item and location must be maintained either at the detail level or by grouping similar items and locations into categories.  An example of item characteristics at the detail level would include exact dimensions and weight of each item in each unit of measure the item is stocked (each, cases, pallets, etc) as well as information such as whether it can be mixed with other items in a location, whether it is rack able, max stack height, max quantity per location, hazard classifications, finished goods or raw material, fast versus slow mover, etc.  Although some operations will need to set up each item this way, most operations will benefit by creating groups of similar products.  For example, if you are a distributor of music CDs you would create groups for single CDs, and double CDs, maintaining the detailed dimension and weight information at the group level and only needing to attach the group code to each item.  You would likely need to maintain detailed information on special items such as boxed sets or CDs in special packaging.  You would also create groups for the different types of locations within your warehouse. An example would be to create three different groups (P1, P2, P3) for the three different sized forward picking locations you use for your CD picking.  You then set up the quantity of single CDs that will fit in a P1, P2, and P3 location, quantity of double CDs that fit in a P1, P2, P3 location etc.  You would likely also be setting up case quantities, and pallet quantities of each CD group and quantities of cases and pallets per each reserve storage location group.  this sounds simple, it is…well… sort of. In reality most operations have a much more perse product mix and will require much more system setup.  And setting up the physical characteristics of the product and locations is only part of the picture.  You have set up enough so that the system knows where a product can fit and how many will fit in that location.  You now need to set up the information needed to let the system decide exactly which location to pick from, replenish from/to, and put away to, and in what sequence these events should occur (remember WMS is all about “directed” movement).  You do this by assigning specific logic to the various combinations of item/order/quantity/location information that will occur. 
Below I have listed some of the logic used in determining actual locations and sequences.  
Location Sequence.  This is the simplest logic; you simply define a flow through your warehouse and assign a sequence number to each location.  In order picking this is used to sequence your picks to flow through the warehouse, in put away the logic would look for the first location in the sequence in which the product would fit.  
Zone Logic.  By breaking down your storage locations into zones you can direct picking,  put away, or replenishment to or from specific areas of your warehouse.  Since zone logic only designates an area, you will need to combine this with some other type of logic to determine exact location within the zone.  
Fixed Location.  Logic uses predetermined fixed locations per item in picking, put away, and replenishment.  Fixed locations are most often used as the primary picking location in piece pick and case-pick operations, however, they can also be used for secondary storage. 
Random Location.  Since computers cannot be truly random (nor would you want them to be) the term random location is a little misleading.  Random locations generally refer to areas where products are not stored in designated fixed locations.  Like zone logic, you will need some additional logic to determine exact locations.  仓库管理系统英文文献和中文翻译(2):http://www.751com.cn/fanyi/lunwen_40639.html