Composers, particularly in the 20th century often make use of changing time signatures frequently in a piece of music. Composers such as Stravinsky use this technique to great effect.
Follow this score of 'Sacrificial Dance' from 'Rite of Spring' by Stravinsky where you can see the different time signatures for the bars of music.
The music begins in 6/8 time for the introduction and verse. At around 37 seconds the music changes to 5/4 for the chorus and instrumental bridge, returning to 6/8 for the verses.