2.) When should you choose the fields directly from the Database, and when should you use the Command feature? What are the pros and cons of each??
-------Using “Command” you can write your own sql for data/data manipulation.
Yes and no. You can create a running total that only gets evaluated on certain conditions, you can create a formula using shared variables to act like the SUMIF, but there is no SUMIF function in crystal.
The command feature (as stated by listener), you can more control what fields are seen by the report (and if you are really good with SQL, can do some neat tricks). Also if you have a where clause in your command, then you will not be bringing in all the rows into crystal for it to process. Using the tables and linking fields is faster and easier to understand for development. But normally the report will process faster with a command.