Transitions http://zerosixthree.se/8-sass-mixins-you-must-have-in-your-toolbox/

sass-transitions-mixin.scss

@mixin transition($args) {
  -webkit-transition: $args;
  -moz-transition: $args;
  -ms-transition: $args;
  -o-transition: $args;
  transition: $args;
}

sass-transitions-usage.scss

a {
  color: gray;
  @include transition(color .3s ease);
  &:hover {
    color: black;
  }
}

As with animations, transitions also make your code quite bloated which can hurt the readability. But this is also solved by using a mixin for it.