Opening Bid: Three Hearts or Three Spades

If you like to open three of a major with a very weak suit and perhaps 6 points, you won't like this agreement.  Bridge players evolve... Early in their playing they seem to stay with the recommended sorts of hands, and then when they see how effective a preempt can be, they start shading the requirements.  They also start playing more doubled contracts!  Have you noticed that after a few years they seem to regain their conservativism?

As a note... The bridge-playing robots on Bridge Base Online use very sound 3-level bids.

Opening Three of a Major
The recommended guide line is to hold 8-10 points and at least a 7-card suit, with most of the points in the major.   This hand is an example:

   7 4
   K Q T 9 5 4 3
   K 3 2
   8

If partner can depend on you for a good suit the bidding is much more constructive and he can usually make an informed decision as to the final contract.  And if you play it, you are not nearly as likely to have to play it doubled.