A washer platform is simply a pedestal for a washer to rest on. Raising the level of a front-loading washer makes using the machine more ergonomic.
Using a front-loading washer can be hard on a person's knees and back because the washer door sits low on the ground and using the machine requires constant bending and lifting. A platform elevating the washer helps minimize the exertion involved.
A washer platform also provides space beneath the appliance for laundry bins or other storage. The Contractor Kurt website provides illustrated instructions on how to build a sturdy, attractive washer platform for less than $500 as of February 2015.