The most skilled men of our town serve at the Workshop. They improve our troops and war ships equipment with the latest inventions. May they become even better and stronger! Every stage of improvement allows you to get more upgrades for troops and ships.
The benefits of the Workshop apply retroactively to all of your existing units and ships, as well as to those trained later. They also apply to all of your colonies, regardless of whether you have a Workshop in that colony.
If the Workshop is demolished, all the acquired upgrades will be kept. So when all upgrades have been made, the building becomes useless and can be safely demolished. Having more than one Workshop built in your empire allows for simultaneous upgrades (one upgrade per Workshop).
There is no need to build your Workshop beyond level 28, as you can learn all upgrades for allunits and ships at level 28.