I recently installed GGTS. It's been good so far but it's starting to annoy me how the dashboard (window) keeps showing up on start up. I checked the preferences but there's nothing there that switches it off. I attempted to uninstall the feature, but the GGTS won't allow me.
You are probably running into this bug: STS-3935. The dashboard is supposed to stay closed when you close it, but in some situations in STS 3.6.2 it doesn't.
If you upgrade to a newer version of STS the problem should go away. If you do not want to upgrade your STS, you can also try running with JDK 8 (so you'll get the new dashboard which is not subject to the bug).
Or, another workaround suggested in the bug-report is to open manually edit the preferences file at workspace/.metadata/.plugins/org.eclipse.core.runtime/.settings/org.springsource.ide.eclipse.dashboard.ui.prefs and add or change the line:
org.springsource.ide.eclipse.dashboard.uidashboard.startup=false
Read the bug report if you need more details.