You can also add a buss track and apply an effects automation envelope, which will let you fade the effect in and out throughout the course of the track, effectively letting you turn the effect on for specific events, or adjusting how much of the effect is used from moment to moment.
Or, you could put that event on it's own separate track.
edit ... Hmmm, on second thought, i'm not sure if VMS 4 has effects automation. But, the other two methods i mentioned will still work.
I often will put the reverb plugin on the track, but automate the reverb "return" or "level output", allowing it to be heard only during the section where the particular clip is located.
A non-realtime effect is a destructive effect ... meaning you add it permanently to the sound file. Personally, I find that bad workflow. However, adding audio to a track, using the effect you want, and then rendering the track with effects makes sense. This way your original media stays intact, and you have the 'frozen" track (with FX) that frees up the proc to do other things.
Using the "Apply Non-Real-Time Event FX..." option in Vegas does not destroy the original wave/audio file.
When you use this option youare presented with a save as dialog to save the processed file. The name that Vegas builds will be appended with a take number. After you are done rendering this file, it is added to the event as a new take, set as the active take and you are ready to go. You can then switch between the "processed take" and the original all you want with out ever loosing your original media.
Additionally, you can use the Open "copy" in Sound Forge option that does essentially the same new take feature.
There are many cases where offline processing is preferable to real-time. Many convolution process or high quality pitch shift plugins cannot really be handled in real-time.