As hockey players get more and more competitive the trend towards dryland hockey training to suppliment regular practices and games has increased. I think back to the famous Canada vs. Russia series of 1972 and remember how the Canadian team was in far worse shape than their Russian counterparts who used extensive dryland hockey training and arrived in Montreal in far superior condition. Back then NHL players would take the summer off and then use training camp to try to get back into shape.
That has all changed, most serious hockey players both professional and amateur have an off season regiment to maintain conditioning and improve skills. Depending on where you live you may have access to hockey rinks all year round, but even if you do their may be limited availability and of course the cost for ice time. Hockey training on dry land allows you to control your own schedule and regiment and can build on some types of skills such as strength and flexibility. Ultimately though you are limited with dryland training on development of hockey specific skills.
The development of affordable synthetic ice has changed that. Now you can supplement your dryland hockey training with on ice work without being limited by the schedules and availabilities of public rink facilities. Skills like skating, stickhandling and shooting are difficult to accurately simulate without being on skates. Synthetic ice allows you to work on the exact same movements and muscle groups as real ice. It has revolutionized the meaning of dryland hockey training.