AllowZeroLength Or Not

I've been at this for quite some time now; creating databases and applications for a small company. I have gotten along ok by studying various books, with the gracious help of many exceptionally knowledgeable people in this forum, and by making heavy use of the archives here.

I have moved on, however, having found what many of us would likely consider a dream gig. I am now part of a team which will develop an application and associated database which we will make available (sell) to other companies. Pretty scary, considering I have no formal training, but I intend to make the best of it.

I of course want a solid foundation, and have a basic design question:

Briefly, which things should one consider when deciding whether to allow zero length on a text field?

And a related question:

I have in the past set AllowZeroLength to No, primarily because my installation(s) of Access have always defaulted to No.

In my current installation (2003), it defaults to Yes.

How can the default be changed?

I found the same question posted in the archive, but nobody replied to the post.

Thanks, and may I just extend at this point my deep gratitude to those who have been so willing to share their extensive knowledge and invaluable experience with everyone.