Nothing different happens, which may be unexpected at first – typically there is a big difference between literal values and transcluded values, as we've seen in Ex:QuotedMacroCall and Ex:WikifiedQuotation. The reason it's different here is that the text attribute of the $wikify widget is treated as wikitext. So if we give "<<someVariable>>" as the value, the first thing TiddlyWiki will do is wikify that text, which will result in the value of someVariable. Then TiddlyWiki will wikify that again as long as it still contains wikitext that can be transformed. Leaving off the quotation marks saves one round of wikification by directly passing the value of someVariable to the widget, but the end result is the same.