Laying structure for large endian and small machines

I go through the compiler, takes care of the alignment, as indicated in the following link.

http://vcfaq.mvps.org/lang/11.htm

I summarize my question, in which scenarios should we programmatically build, and which compiler script will do for us?

Is padding required if two machines with different endian types, i.e. one m / c is large finite, and the other is a little oriented and transmits via TCP / IP, is this necessary for filling?

Please clarify my question.

Thank!