[This post was first published on 27 April 2011.]
It depends. The purpose of a significator card is to add structure to a reading, which may or may not be necessary depending on the spread used and the reading question.
However, regardless of the spread and question, when a reading potentially involves several people I believe it is helpful to decide in advance who the Man and Woman cards will represent if they show up in the reading.
I can fully understand why significator cards are used in a Grand Tableau (big picture) that incorporates all 36 cards and is usually a general forecast of the sitter's life for a specific period of time. The significator cards allow the reader to easily identify specific persons in the reading and to zoom in on different aspects of the sitter's life.
Lines of 3, 5 or more cards include one or more cards on either side of the significator card that represents the question topic. This spread is suitable if one is interested in a Past-Present-Future timeline and when describing a person or place.
One can simply lay out a few cards in response to a specific question and only take any significator cards into account if they show up. This reading approach is simple and highly effective for a quick reading that does not necessarily involve a Past-Present-Future timeline.
Is it necessary to charge significator cards used in Lenormand readings?
I have included my significator associations for various Lenormand cards in my Lenormand dictionary.
[Card images: Modern Minimalist Lenormand by Melissa Haney licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License]
[You may also be interested in reading Jason's related blog post, Charging a Key Card.]