PNG Images are one of the most used format as they are widely supported as well as one of the best ways to format transparent images. Drawback being these file formats can be relatively bigger in size. If the images files are bigger, consequences are it will slow down the loading of websites or apps.
TinyPNG
This is where tinypng comes to rescue. Tinypng helps to reduce the size of png files by using compression technique called lossy compression technique.
In my real web development cases , I had compressed the png upto 60% in size reduction using tinypng, which had resulted in decreasing the page size quiet significantly and hence boosting up the page loading time.
There is a free drag and drop tool at the website if you want to test how much of size you can reduce using tinypng. And also if you are willing to use it regularly there is a Photoshop plugin too. Details about tinypng can be found here.