>But, I just found out that mostly every object has such property, but I would like to ask UT users where they used this property. Is it usefull? Maybe there is some function getObjectByTag?

As the others said, you can keep any string in there. I concur with Hilmar that it is generally better to use your onw custom property with a descriptive name. That said, I use Tag only when I need to change a tooltip at runtime, depending on some condition, and later I want to return the tooltip to default.

What I do then is in INIT() I copy the default tooltip (generally set in the properties window) to Tag so I can restore it anytime from there.

HTH