I was wondering whether having an index page that says under
construction please check back periodically is worth being indexed and
crawled by search engine bots...

do you think this could hurt when i actually release the web site? or
should i allow bots to be able to crawl and index from day one?

Don't do it. Don't let them crawl the site before it's actually
finished.

This is no old wives tale.

They come by once, see next to nothing worth indexing, index what
there is (zip) and won't come back for a long time as they have
already classified the site as being basically empty.
To get them to come by and crawl again you will need some good
backlinks at this point, as you'd have wasted your one chance to get
indexed right out of the box. You'll still need the links later, mind
you, just to stay indexed properly, but every new site gets an initial
boost, when it's most important to start being visible so that you can
start acquiring those precious backlinks.

On Aug 2, 10:32 pm, PaulC wrote:

I think Webado's advice is pretty much right on, especially if the
whole site is not ready yet. However, if you already have the domain
name, then it makes sense to at least put up a holding page for the
site, so that people know that they've reached the right address. To
prevent indexing of that holding page, you could return a result code
503, which will tell the search engines to come back later.

One thing I would recommend not doing is to use a domain parking
service with automatically generated pages full of ads. When visitors
(or search engines) visit your site and see that, they might assume
that the domain name is not going to be used for a normal website. If
search engines crawl and index those pages, it may be confusing for
them to later find out that those URLs are not being used and not
being redirected.