Ease of use, intuitive interface and ability to share maps with colleagues who are not familiar with software such as ArcMap or QGis. Sometimes it can take longer than expected for WMS layers which is frustrating especially when dealing wtih large datasets. I would recommend this product if you need an easy way to view your own mapping/geospatial information but also have access to other users' views without having to download multiple copies of files. We use Mapviewer within our organisation where we create geodata that helps us make informed decisions about our business operations.