As per AACE® International Recommended Practice No. 84R‐13

Use of Extended Shifts or Planned Non‐Work Days as Make‐up Days
The use of planned non‐work days (often weekends and holidays) to make up for lost weather time on critical or near‐critical path work is a popular methodology for contractors because it is simple and requires minimal work to implement, but does not reflect effective weather planning. The approach can be appropriate when the climate does not demonstrate large variations in adverse weather. In this discussion, a five day workweek is assumed with weekends providing planned non‐work days.
Problems with this approach include:
• The weekend may not provide adequate replacement for situations where required planned non‐work days exceed the number of weekend days, or where adverse weather occurs for more than two consecutive days.
• As the project nears completion weekend weather mitigation work is less likely to suffice for recovery from the time lost due to weather.
• An owner may take the position that the contractor has planned for two days of adverse weather in each five‐day workweek.
• Due to schedule constraints, weekend days may not be available to allow for make‐up time.
• Overtime premiums for craft and supervision may be required when weekend work is necessary.
• Owner furnished supervision or oversight should typically be available if weekend work is required.
• Inspections by owners or local jurisdiction may not be available to inspect on weekends.
• Weekends may not account for seasonal variations.
• Reduces the contractor’s opportunity to use weekends to mitigate low productivity periods caused by non‐weather related issues.
• Poor morale and fatigue issues leading to worker safety and productivity problems if weekend work occurs over multiple weekends in a row.

Ironically the  AACE® International Recommended Practice No. 84R‐13 does not suggest how to model the seasonal variations of productivity on all remaining work days, an impact that many times has more impact than actual "lost days".  We all know productivity when temperature is 70F is usually higher than when temperatoure is 40F, work is not stopped but production rate decreases, activity duration increases and might require different crew composition, any schedule model blind to this is a poor model.

At home this is a requirement mostly in goverment contracts. That it is not required does not means you shall consider the impact of weather in your planning.  It is not good enough to only consider a few adverse weather days and omit the effect of adverse weather on the remaining days.