BeginInvoke is used to execute the delegate on a threadpool thread.
DynamicInvoke, IIRC, is just a convenient way of invoking a delegate
without knowings its type. You could do, for example,
Delegate d = new SomeDelegate(SomeMethod);
d.DynamicInvoke(new object[] {param1, param2})

instead of
SomeDelegate d = new SomeDelegate(SomeMethod);
d(param1, param2);

DynamicInvoke is useful when you don't know the exact signatures of the
methods in advance.

Every call to BeginInvoke must be accompanied by EndInvoke. You'll leak
resources if you don't. What's more, if the method threw an exception,
EndInvoke will cause it to be rethrown, so if you don't call EndInvoke,
you'll never know if the method executed successfully.

Regards
Senthil