Since CSS animations were introduced back in the early 2000s, most other browsers have come on board with support. With the keyframes in the CSS3 animations module also allowing timings and more advanced properties, it’s amazing what web standards can accomplish.
Ever since our caveman days, the human eye is excellent at noticing movement, which is why animation, when done well can be so effective in modern well-designed applications.
Even in situations where you have a lot of text, animating things like illustrations can really being the content to life, like in this lovely XBox One review on Polygon.
However unless you are creating something purely for entertainment, animations should be kept short, to let users get on with the task at hand, especially if present on a much-visited element of the UI. The key is to use it to enhance rather than take over an interface.
Don’t use animation for the sake of using animation. Excessive or gratuitous animation can make people feel disconnected or distracted, especially in apps that don’t provide an immersive experience.
Be realistic and strive for credibility. If a user opens a menu by swiping down, then they should be able to close it by swiping up.
Animation has several different uses within modern web and mobile applications, such as:
Showing loading states
Assisting with wayfinding
Guiding attention and focus
Conveyance of brand, voice and tone
...and I'm going to cover a few below, with the help of my favourite Marvel superhero.
Historically animation has been used for things like the much abused and ubiquitous spinner, useful when you are loading something else that might take a little time - in this case it just repeats until the content is loaded in.
The problem with this is that a never ending spinning circle can cause people to think a system has stopped responding.
An alternative to the endless spinner is to use Skeleton states. Skeleton screens are used by several companies to good effect, to improve perceived loading speed, by presenting an intermediary placeholder structure instead.
Both Medium and LinkedIn use skeleton structure to good effect.
Not only is this nicer to look at, but this helps with user understanding by showing the structure of something before it is loaded. My example below:
Granted, technically the only animation is a subtle CSS animation of the skeleton background colour, but I think it's a nice touch to show something is incoming, and the gradual replacement of content is animation in itself.
Attention and focus
Animation is very good for highlighting things like buttons and adapting form fields when things are added or changed. Apple do a great job of this with their search box.
A nice example of this is the floating label pattern, that uses the form label as a placeholder text, and then floats this above the form field when the field is focused. It's subtle, but nicely and cleanly done using just CSS transitions and transforming using translateY, and shows the user subtly which fields have been completed, and which are yet to be filled.
CSS animation can also be used when validating forms to great effect as people fill it out for more immediate feedback.
We all know famous digital brands that we can recognise by recognising a part of their user interface. As well as voice and tone of copy, animations can really help cement what a company is, through ensuring things like the speed of animations match their personalirt (using things like easing functions to change how animations behave). Changing these can add to a sense of fun in some cases, or seriousness in another - there's a great article with further details here.