When to actually use Time.deltaTime?

[jaunty forge]

So I've been making (mediocre) games a decent amount of time and I still don't exactly understand this aspect of coding.
When should I be using "Time.deltaTime"?

For example, do I use it within fixedUpdates? And what about jumps? Should the force used for those be multiplied by it or no? I just really am confused on when it should and shouldn't be used lol! If anyone can explain, that would be awesome!

[nova hearth]

if you're changing a value over a series of frames you typically want to to do it independent of framerate, thats when you usually would use it .. In update , say you got a timer value that increases timer += 1, to not make people with higher frames increase timer faster than people with lower frame rates, you would add timer += 1 * Time.deltaTime
it would account for the frame rate difference "delta" in time

[jaunty forge]

Ah, so Time.deltaTime is really just to keep things the same framerate? But the one thing I am still not entirely certain on is its use in fixedUpdate. Thanks a bunch!

[nova hearth]

kinda. its to help account the difference in time between frames to keep things consistent, it doesn't itself do anything but give you the time it took from the last frame to this frame

when used inside FixedUpdate it turns it already into Time.fixedDeltaTime which is instead using fixed rate, same as FixedUpdate

[jaunty forge]

oh, so it turns into is own new thing entirely?

[nova hearth]

further info more specific in docs too
https://docs.unity3d.com/ScriptReference/Time-deltaTime.html
https://docs.unity3d.com/ScriptReference/Time-fixedDeltaTime.html

[jaunty forge]

oh sweet! thanks!

[nova hearth]

instead of frames, its fixed physics tick rate which is what physics are sync to

https://docs.unity3d.com/Manual/fixed-updates.html

[jaunty forge]

Okay! That is actually really helpful! Thanks a ton!

[upbeat mountain]

in short yes, it's the time period between last frame and the current frame.

on frame-based game engine such as unity, deltaTime commonly used to make sure things in your game don't run out of sync from the engine's frames

[foggy hedge]

another perspective: it's a conversion factor between "x per second" and "x per frame"
if you have a value in "x per seconds" and you need to convert to "x per frame" (such as changing a value over time in Update) then that's where you would use deltaTime
fixedDeltaTime is similar, but for "x per physics tick" instead

[errant ruin]

I would say it's the opposite of this. You cannot keep things the same framerate. It's to keep the game behaving the same way from the user's perspective regardless of the fact that it's running at a different framerate every time.