The Microsoft .NET Framework 4.0 full installer (32- and 64-bit) is 48.1 MB and the Client Profile installer is 41.0 MB. The extracted installation files are 237 MB and 194 MB respectively, and once installed, they are 537 MB and 427 MB.
This is a difference of 110 MB. What difference is there between the two packages?
When is it preferable to install the Client Profile instead of the full .NET Framework?
You should deploy "Client Profile" instead of "Full Framework" inside a corporation mostly in one case only: you want explicitly deny some .NET features are running on the client computers. The only real case is denying of ASP.NET on the client machines of the corporation, for example, because of security reasons or the existing corporate policy.
Saving of less than 8 MB on client computer can not be a serious reason of "Client Profile" deployment in a corporation. The risk of the necessity of the deployment of the "Full Framework" later in the corporation is higher than costs of 8 MB per client.
Cameron MacFarland nailed it.
I'd like to add that the .NET 4.0 client profile will be included in Windows Update and future Windows releases. Expect most computers to have the client profile, not the full profile. Do not underestimate that fact if you're doing business-to-consumer (B2C) sales.
A list of assemblies is available at Assemblies in the .NET Framework Client Profile on MSDN (the list is too long to include here).
If you're more interested in features, .NET Framework Client Profile on MSDN lists the following as being included:
And the following as not being included:
What's new in .NET Framework 4 Client Profile RTM explains many of the differences:
However, as stated on MSDN, this is not relevant for >=4.5: