I am one who believes /testing should be enabled routinely. Some caution is needed, however.
Note that in Gslapt the COMMON tab indicates the source of the file. I think everyone should check what the source is whenever they select a package to install. If it says /testing, remember that it's a package that hasn't yet been generally released. If you're willing to test, download it. If you're not, skip it. But do note the repo source of packages you select.