A piece that is truly in free time — where there is no regular ("metered") pulse — either omits bar lines or uses them to indicate phrasing. Dotted or partial bar lines are sometimes used to help circumvent a regular bar line's association with meter and downbeats.
In a piece that has a regular pulse but irregular pattern of emphasis, then it's okay to omit the time signature and use bar lines to delineate the phrases/emphasis points. Again, dotted or partial bar lines can be used if there are lesser emphases within the larger phrase/bar. This is especially helpful for long phrases. Elaine Gould in Behind Bars offers the example of a measure with 21 beats, subdivided by dotted bar lines to assist with placement of emphases and to help to eye keep track of where one is in the score (p. 178).
Another possibility is to include time signatures that are just a single numbers indicating the beats in the particular unit. This can be a useful cue when reading.