Showing Two Suits Theory

There are two strong reasons for showing 2 'objects' with a single bid:

Time & Safety!

Explanations later - lets get to see the examples first!

By objects we could mean any of the following depending on context:

Let's list the numerous places where all these can be found in BetaACOL:

Strong 2-suited overcalls      Used after opponents open the bidding. May be used as an immediate overcall or in the protective position: shows 2 suits usually 5-5, and a  4-5 LTC
Weak 2-suited overcalls         Also, used after opponents open the bidding. May be used as an immediate overcall or in the protective position: shows 2 suits usually 5-5 and a 6-7 LTC
CDH                                                Used when opponents open 1NT in the 12-15 range. Shows two 4+ card suits including the suit bid. Usable as overcall or as a protective bid
Protective New Suit                                                  Re-opening the bidding in the protective position after opponents open 1 of a suit followed by 2 passes. Shows 2 specific 4+ card suits including the suit bid
Responding to a T-O Double   Going to the NEXT bidding level - shows two suits including the suit bid
Inverted minor response       New suit shows a guard & a guard in the next suit
Major suit trial bids                  Asks help in the bid suit &/or the higher suit

In all these cases the detailed texts need to be understood for their usage.

The first two are the most well known of this list. A little different to what you may be used to nevertheless.:
CDH is an interesting defence to the weak NT as it enables get-out in any suit the lowest rnaking being shown - then 'wriggle'
    E.g. 1NT - 2D  denies Clubs, Shows Diamonds & at least one of the Majors.
The protective 'New suit' is easy & interesting:
     E.g.  1H(opponent) P P 2D   Shows both Diamonds & Spades
       A single suit can be shown if 6 card  but un-ambiguously:  1H(opponent) P P 2S3C
T-O Double responses are totally a different approach - part of which show two suits - this needs careful study
       E.g. 1H(opponent) *(partner) P 2D Shows Diamond & Spade suits, again a bid of 3D would show a 6 card suit not forcing & 2H would indicate a minimum of a small openin  g and a good suit in a single suited hand
Inverted minor response is Forcing. Opener's preference for a rebid is any suit showing a guard in that suit and the next higher suit too.
Other sequences  are available for other hands.
         E.g.  1D - 2D - 2S..... shows guards in the black suits & denies a guard in Hearts
Major suit trial bids.  A new suit by opener requests help in that suit and the immediate higher ranking suit.
          E.g. 1S - 2S - 3H... Asks support: top controls or shortages in Hearts &or Clubs   (1in other words 1st or 2nd round controls).
           E.g.  1S - (2H opps) -  2NT(good raise to 3) -  3D(opener asking) -  3S  (no help in  Diamonds  & Hearts) or  4S (i have help)

Now the win-win of this style of bidding!

TIME. Todays game is most competitive and if your methods only allow you to show 1 suit (probably the Major) then there is a very good chance that there will not be the TIME or bidding space to announce your 2nd suit. With Beta's style of bidding you get the two off your chest straightaway.
SAFETY. Simply this the chance of finding a fit naming just one suit is 25 - 35% the higher figure with a 5 card suit. With two suits: 4-4 or 5-4, the probable fit liklihood is a seriously more healthy 65 - 85%.The cost of not finding a fit can lead to a more probable negative score.

By focusing on 2-suits whenever possible we may fail to emphasise length in a trump or even the existence of a side suit in a weak hand by not being able to declare a side suit (more likely a minor)