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?
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: