[BaggyBomber]

1) Playing with 3 centre backs is a good way of giving your team possibly a spare man at the back as well as a spare man in midfield and 2 strikers upfront. The 3-5-2 for example gives a spare man at the back and a spare man in central midfield which is a great way of playing against a normal 4-4-2. However, playing with 3 centre backs is not useful against teams playing with 1 striker. A 3-5-2 up against a 4-3-3 for example doesn't give a spare man in midfield, leaves 2 centre backs not marking anyone, it can cause havoc against teams who play with flexibility and leaves the 2 wing-backs 1v1 against the opposition wingers.  

2) In modern day football, most teams now play variants of 4-2-3-1 and 4-3-3. The days of most teams playing a basic 4-4-2 like you described are gone. There are still teams who can play 4-4-2 successfully (Albion showed it under Pulis) but generally 4-4-2 is slightly outdated in it's set-up. 4-4-2 has been such a popular formation for the past few decades that every type of 4-4-2 with individual tactics has been worked out by coaches both present and past.

3) Coaches in modern day football have had to learn to be adaptable. Using just 1 formation all the time is never always a good idea because different matches need different formations and tactics. For example, you wouldn't play a 4-4-2 away at Barcelona just like you wouldn't play with 3 centre backs either. For a team like Barcelona, a 4-1-4-1 or 4-3-1-2 formation is usually a good bet to match them up in midfield. On the flip side, if you were playing against the bottom of the league team who are a playing with 3 centre backs and 2 wing-backs (Hull and Wigan in recent years) then playing a 4-4-2 could work because you have 2 strikers against their 3 centre backs. A lone striker can easily be outnumbered, outmuscled and outthought by 3 centre backs.

Sorry about the above answers being a little long but I hope they answer your questions Wille.

Thank heavens I never realised footy was so complicated when I played, at a reasonable amateur level, if I say so myself, in schools, works and Sunday league football for twenty five years.  The mental stress would have been too much.  Even thirty five years ago, though, we still had eleven v. eleven on the pitch!