Yes, it can help in most cases. However, it's not the only option that can be used to speed up work on slow connections. Other options include:
- Color depth.
- CPU Usage.
- Disable aero and remove wallpaper.
You will find all these options in Connection Properties. Connection properties are individual for each remote connection, but they can be modified en masse.
Also, you can set defaults (in Viewer, select the Tools tab and click 'Default connection properties' button). In the default connection properties dialog you set the properties that every newly created connection will have from now on.
You will find more information on working with the address book and connection properties in the section Using Remote Utilities -> Connection List -> Managing Connections of the User Manual.
Forgot to add that there is certainly a reasonable "threshold" of connection speed/quality. For example, it's hard to recommend anything if the connection method in question is EDGE or 3G on a mobile network :) We are developers, not wizards :D