The National Electrical Code states as follow:
(B) Expansion, Expansion-Deflection, and Deflection Fittings. Raceways shall be provided with expansion, expansion-deflection, or deflection fittings where necessary to compensate for thermal expansion, deflection, and contraction.
Informational Note: Table 352.44 and Table 355.44 provide the expansion information for polyvinyl chloride (PVC) and for reinforced thermosetting resin conduit (RTRC), respectively. A nominal number for steel conduit can be determined by multiplying the expansion length in Table 352.44 by 0.20. The coeffi‐ cient of expansion for steel electrical metallic tubing, intermediate metal conduit, and rigid metal conduit is 1.170 × 10-5 (0.0000117 mm per mm of conduit for each °C in temperature change) [0.650 × 10-5 (0.0000065 in. per inch of conduit for each °F in temperature change)]. A nominal number for aluminum conduit and aluminum electrical metallic tubing can be determined by multiplying the expansion length in Table 352.44 by 0.40. The coefficient of expansion for aluminum electrical metallic tubing and aluminum rigid metal conduit is 2.34 × 10-5 (0.0000234 mm per mm of conduit for each °C in temperature change) [1.30 × 10-5(0.000013 in. per inch of conduit for each °F in temperature change)].
The key words here are "where necessary".
In Michigan we have even greater temperature swings and I have never seen an expansion joint on an underground lateral.
Not a bad idea necessarily, but unless required, I wouldn't spend the money unless you are really worried about frost heave.