There are different options for automating workers:
-*simple* automation (by clicking on button while worker is active or hitting a) lets the worker become totally self-governed; they might consider an existing improvement on a tile as useless, thus changing it. Example: You've intentionally built a mine on a grassland tile with a manual-steered worker to increase shield accumulation at a low-shielded city site. The automated worker could decide to change this mine to irrigation. It's not only time consuming, but also makes a botch of your plans.
-shift-a workers don't change existing improvements; note that the term *improvements* also includes jungles,forests, but not roads! Roads could be changed to railroads by shift-a workers. These workers will never get *active* again, unless you click on one. Later in a game, they stay in cities and will automatically move out to clean pollution.
-to get rid of jungle/forest:
-forest: do it manually, for the reason of an opimal timing of the production
boost (the 10 shields added to prod box after chopping down)
-jungle: use shift-j (only in vanilla civ3! -don't know the PTW order) to
autoclear all jungle tiles in your cultural borders. A shift-j
worker will get active, when last jungle in your actual territory
is gone.
There are also other automating options, e.g. "build railroad to location". Keyboard shortcuts are listed in manual and somewhere in the pedia. Of course, it's always best to micromanage all workers and a must in early game. Be careful, automated workers might take the risk of improving tiles in dangerous areas due to wartimes.
But even if you decide to automate workers, have also some manually-steered around. 50% on shift-a (when railroads come up) is a good portion (total: 1 worker per city) for a medium-level-lazy like me.
