Overall: Lua can only get input as text strings passed to the <precode><nowiki>{{#invoke:}}</prenowiki></code> and what can be fetched via frame:expandTemplate, frame:preprocess, and the like. Lua on Wikipedia can only output wikitext not including pre-save transforms or transclusions and other <code><nowiki>{{...}}</nowiki></code> constructs. Also, all Lua in the page is limited to 10 seconds CPU time (you can look in the source code of a rendered page to see how long a template or module took to parse). And relative to standard Lua, Scribunto's Lua lacks all sorts of functions (see [[mw:Extension:Scribunto/Lua reference manual#Differences from standard Lua]]).
