If you've installed many extensions and apps, it's likely that the Extensions folder from your Chrome profile uses many hundreds of megabytes. Some apps are pretty big now: for example, the latest version of Polycraft uses 76.6 MB. It's obvious that a single application could use 1 GB after a few updates.
Here's another example: the LastPass extensions. I've checked my profile folder and Chrome keeps 11 versions of this extension since October 2013. Total disk usage: 107 MB, instead of 9.6 MB for the latest version.
Obviously, the old versions are useless and this is a bug. There's a bug report from a Google employee here and it mentions that "the Google+ Photos app is a fairly large app (56MB) which updates frequently (weekly?). It does not appear that older versions get deleted. For the G+ photos app which takes 56MB, I had over 700MB of old versions on my drive."
Until Google fixes this bug, you can manually delete the old versions. Go to your profile folder and open the Extensions folder. Every extension and app has its own folder with a cryptic name (the extension ID), so you can open each one and delete all the subfolders except for the most recent one. For example, LastPass's folder is named hdokiejnpimakedhajhdlcegeplioahd and it has a subfolder for each version. You can sort them by name or by date and keep the most recent version (3.0.22_0).