In Samplitude you have the choice to "Scan VST folders for new plug-ins" only. This is very fast and convenient when you only added a new one. But if you have Waves plugins there is always the shell that has to be scanned and that is time consuming. I see the difference with or without Waves shell quite well, because I have the Waves plugins only on one of my PCs.
In Sonar/CbB there is also a setting (Rescan existing plugins = off) to scan only for new ones, but I have the feeling it is not always considered and it is also not so efficient like in Samplitude. And if you start scan directly in the Plugin Manager, then it is never being considered (that's why I got used to scan in Preferences only).
Another reason why I dislike the Waves shell is that you do not have the possibility to organize plugins in your way. This is crucial for Samplitude, because it has no real plugin manager. So I have created an own VST2 plugin folder for Samplitude with logical subfolders like "Reverb" and in there I have only links to the real plugin DLLs (mklink), runs great except for Waves plugins! I even reorganized the VST3 folder like that, but just kept the top in the standard location and used the real DLL files.
Marc