Lookmarks, analog to bookmarks or landmarks, save the position and angle of your camera. After setting a lookmark with the Spyglass, you will be able to go back to that exact same view angle you had when you saved the lookmark.
To inspire you for what lookmarks can be used, I have compiled an non-comprehensive list of scenarios.
/17 <New Lookmark Name>in local chat, where <New Lookmark Name> is to be substituted with a name of your liking (without the "<", ">"). (Note that this only works immediately after you have saved a lookmark. If you want to rename a lookmark later on, please read Managing Lookmarks below.)
There are a number of ways to focus a previously saved lookmark:
Before focusing a lookmark, make sure, however,
that your camera is in the default mode. Press the
Esc key to make it go there. (If your camera is not
in default mode, your viewer's camera controls will override any scripted camera controls, i.e. the Spyglass won't be able
to focus your camera.)
Clicking the "Lookmarks mode" button will set the Spyglass into the lookmarks display mode. The lookmarks in the current region will then displayed above the Spyglass.
Next to the name of a particular lookmark you will see four action buttons:
Note that whenever you focus a lookmark you will find an SLURL to the position of the camera in local chat. You could easily teleport to that location by clicking the SLURL in the chat history window.
Clicking the Menu button, then choosing "Lookmarks" gives you a menu of options for managing lookmarks.
Lookmarks are saved per region. When you teleport to another region you will get a different set of lookmarks. While you can zoom in from a region to a neighboring one, you can set a lookmark that displays a view that isn't actually in the region you are currently in. However, the lookmark you saved in this fashion will only be accessible in the region you saved it.
The number of lookmarks you can set per region is limited by about 50 lookmarks (you might be able to save more). There is no known upper limit for the number of regions in which you can save lookmarks. (Since script memory is limited, there is a limit, but this limit is of rather theoretical nature.)