Been driving for a few decades at this point. I use my turn signals for nearly all turns, and any moving merges. The more information I can give to other drivers, the more likely they are to act rationally.. which decreases the chances of miscommunications and accidents.
I don't always signal while in a turn only lane, as being in that lane should already denote my intentions, and while merging into heavy (stopped, bumper to bumper) traffic..
In a similar vein: