This! The free parking on Sundays and holidays means that parking enforcement officers aren't working.

I think one of the reasons for this is that it's easy to cover a 6-day work-week with only 1 additional worker.

A: M-F
B: T-S
C: W-S, M
D: Th-S, M-Tu
E: F-S, M-W

F: Swing (A's Saturday, B's Monday, C's Tuesday, D's Wednesday, E's Thursday)

A 7-day week doesn't divide nicely. Not to say that it can't be done, but it doesn't divide as nicely.

Likewise, Mass has a history of restrictions and premium pay for Sundays and holidays. Premium pay is being phased out, but it used to require 1.5x pay for a lot of work on Sundays/holidays.

> Unless a non-retail business falls within one of the exemptions in M.G.L. c. 136, § 6, it is not allowed to operate on Sundays. However, for all businesses, a permit for work on Sundays may be issued by the police chief of the city or town where the business is located. A permit may be issued only for “necessary work or labor which could not be performed on any other day without serious suffering, loss, damage, or public inconvenience, or which could not be performed on any other day without delay to military defense work."

I don't mean this as legal advice and I'm sure people could talk about all sorts of loopholes, but my point is that there's a certain expectation of not working on Sundays/holidays in Mass. Even if the law has loopholes, unions representing the parking enforcement would probably be against working on Sundays and it's an easy thing for the city to give them since it's reasonably popular with residents and there's usually a lot less competition for parking on Sundays anyway.

So yea, parking enforcement doesn't work on Sundays/holidays so you don't need to move your car. That doesn't mean you can park super-illegally because the police could still deal with things that are hazards (like blocking a hydrant or parking in the middle of the street).