Thanks Tess! Good point about being able to easily update and add to later.
Most come "out of the box"
not being compliant and then add into that what the user enters, and it can be an ugly mess. IMHO, it is best to do things right, right from the get go. Websites, after all, are where we [need to] put our best foot forward as a business. The coding behind the scenes might not
seem important, but in order for your business to look its best in major browsers, it is
vitally important.
Regarding the freebie website builders, I feel that 99% of them are not compliant. Even though I don't comment on every website review request here, I do run those that use freebie site builders through the validator, and my experience thus far is that almost all do not pass - some more so than others with numerous glaring errors in code.
If your bricks and mortar business needed priming [i.e. compliant coding] before a coat of paint, you're going to do it - so why not do so regarding our web presence and present ourselves in the best possible light?
As an aside: my own site doesn't validate because of amazon widgets.

Makes me want to spit! So it's not just website builders, we also have to be aware of what we add to our sites. I'm working on a fix for my site issues; it's darn irritating!