Optimized Compilation not enabled despite .NET

OK chaps, I've been retired a while, so whilst I know various apps need it, I never really came to grips with .NET, so here's a dumb question, please bear with me.

My B4PPC Desktop IDE always has Optimized Compilation greyed out.

Due to the actions of sundry product installations I now seem to have a grand collection of .NET versions intalled. The list reads thus.....

Microsoft .NET Compact Framework 2.0
Microsoft .NET Compact Framework 3.5
Microsoft .NET Framework 1.1
Microsoft .NET Framework 2.0
Microsoft .NET Framework 2.0 Service Pack 2
Microsoft .NET Framework 3.0 Service Pack 2
Microsoft .NET Framework 3.5 SP1
Microsoft .NET Framework SDK (English) 1.1

Having B4PPC libraries loaded in the project or not seems to make no difference.

So I don't have this IDE option enabled because....?

Am I allowed to delete the older versions of .NET? I seem to recall something about not doing that, but the memory is very hazy!

Since v6.90 the optimized compilation is always disabled and checked. The legacy compiler is no longer available.

Nyaha! I see. Ta.