I ran a disk inventory because I'm running out of space and I found the .metadata folder in my Eclipse (Flash Builder) workspace is 1GB in size. I use maybe 4 of many projects in the workspace. I guess that if I delete it I will have to reimport the projects into the workspace or into a new workspace. What should I do?
The .metadata is the workspace settings storage location. So if you delete it, then all your preferences, caches, which projects are inthe workspace, etc. will be lost.
(To expand on earlier answer).
Yes, go ahead and delete the .metadata. Once you re-import the projects you had, provision your targets, and allow all the indexers to run, you may simply find your .metadata has grown back to the same size again.
One of the few things that won't cause a full regrowth is that you will be ditching your local history per file. This may save a few percent.
On one of my current workspaces, the .metadata breaks down roughly like this (showing only large use folders):
.metadata <- 524 MB
.plugins <- 523 MB (this is where individual plug-ins save there persisted states)
org.eclipse.pde.core/.bundle_pool <- 335 MB (these are the plug-ins that are part of my target platform)
org.eclipse.jdt.core <- 67 MB (this is the indexes of my Java files)
org.eclipse.epp.logging.aeri.ui <- 30 MB (this is the Automatic Error reporting local cache of remote database)
org.eclipse.core.resources/.history <- 12.4 MB (this is the local history)
It may be useful to ask a different question (e.g. Why does foo/bar path in workspace/.metadata take up so much space?) as it may be a simple configuration change has a large impact on your disk usage.