Before giving the answer I would like to provide some information about ST engine
ST stands for Strongly Typed. This is a new scripting engine introduced by Siebel and is available since Siebel 7.7 version. This is default scripting engine for Siebel 8.0
Now, for the answers of the questions
Is ST better than T engine?
Yes, ST is a better engine than T engine as it provides following benefits over T engine
- Intellisense for Siebel Tools
- Improved Memory management and garbage collection
- Improved performance
and several more (but I know only these many 
)
Is it better to typecast variables as in ST?
Yes, it is better to typecast variables
If Yes, why?
Every type of object or variable that we declare has different memory needs or is needed to be treated differently based on the data that it is going to hold.
If we don’t typecast the variables then scripting engine has to decided on the runtime how to manage that variable.
So, type casting reduces overhead of scripting engine as memory needs of a variable can be decided based on its type at compile time, rather than run time.
