Suitcase plug-in cause delay in Photoshop. It is not as annoying as it used to be but still after opening images it takes a few fractions of a second before tools are available. There is also delay in changing tools opening dialogs etc.For one or two images it is not a big issue but if you edit +400 images for a book it amounts to a lot of wating time.
Luckily for me Photoshop plug-in is about useless so I keep it uninstalled. But after an update I sometimes forget to uninstall.
I have used Suitcase for a long time and it has never worked as it should. Nothing much has improved performancewise since long time ago when Mac Suitcase saved information inside the plug-in file itself and after a crash, which happened a lot, the plug-in had to be replaced with a fresh copy. Most user had it ready on desktop. I still use Suitcase mainly because of the font preview.