I got into grunt within the year, I was always aware of it but had never used it in practice. These days I can’t imagine running a project without a task runner. Generally I’ve used grunt for 2 reasons, one is saving me time and two is making my sites faster.

Generally I use grunt to:

Compile my LESS or SASS files and combine into a single file,
Move files from Bower to the public folders,
Combine my organised JS files into a single file,
Minify or Compress my CSS and JS,
Compress images from their source folder to the public folders.