I certainly used to think so.
The thinking was straightforward. If faced with the high calories (or sugar, or salt, or whatever an individual might themselves be focused on reducing) identified by a more realistically portrayed serving size, people might eat less.
Recent research however calls that thinking into question. A study published this year in the journal Appetite found that proposed changes to include more realistic serving sizes led those utilizing them, in laboratory settings, to serve themselves and others more, and that the serving sizes were perceived as amounts that people were supposed to eat.
What the study did not show was whether or not more realistic serving size postings would impact upon the frequency with which people ate a particular product, or whether they might lead them not to purchase certain products in the first place - behaviours which in turn would support the practice.
But those questions aside, the research was pretty clear in that the public's perception of "servings" including the erroneous notion that they were recommended amounts.
Makes me wonder whether or not having a dual column nutrition facts panel that includes a commonly consumed portion amount alongside the whole package coupled with the removal of the word "servings" would help (see up above)?
Future research for someone I'm sure.