First things first, what does 'MOC' and 'MIP' mean? 'MOC' stands for 'Mint on Card' while 'MIP' stands for 'Mint in Package.' These are terms used to describe toys that are still in 'brand-new' condition, i.e., they have never been taken out of and are still in their original factory-sealed packaging. Toys that are no longer in a package are referred to as 'loose' toys.
'MOC' is applied to toys that are packaged with a card behind the toy and a plastic bubble over it. Aside from providing support, the card acts as an attractive background for the toy. The front and back of the card also contain descriptions of the toy inside.
'MIP' is used to indicate the 'brand-new' condition of toys sealed in non-carded packages, although it is also used interchangeably with 'MOC'. There is another acronym, 'MISB', which means 'Mint in Sealed Box', obviously for toys packaged in boxes. There are many other variations - 'MIB' for 'Mint in Box', 'MOSC' for 'Mint on Sealed Card' ... well, you get the point.
OK then, back to the question at hand. Should you or shouldn't you take your toys out of the box? Well, it all depends on why you want to collect toys in the first place. Which will make you happier?
The Value. Many people collect MOC's / MIP's because they do not want their toys to lose their 'value'. It is a fact that taking a toy out of its package instantly and drastically reduces its 'book value' by 50% to 75%. That means that a $10 toy will just be worth $2.50 to $5 once it is out of its factory-sealed package. So if resale value is more important to you than seeing your figures out in the open, then you should collect MOC's/MIP's.
The Space Needed. It is more difficult to safe-keep MOC's/MIP's than loose figures because they take up much more space than the latter. This is not to mention that mishandling one in any way that wears out even a small portion of the package instantly reduces its book value too. Thus, if space constraint and constant handling is an issue for you, you might want to consider just displaying your figures loose on the shelf.
The Look. I personally don't like the look of identical packages hanging on the wall. The toys inside lose their character if displayed this way. But that's just me talking. I've asked other hobbyists and some of them don't feel the same way as I do. Some prefer looking at MOC's/MIP's hanging on a wall to posed action figures on a shelf. Thus, it is all up to the collector to determine what he or she likes to look at.
Yes, at the end of the day it is up to the collector whether he or she wants to collect MOC's/MIP's or loose toys. The important thing is knowing what you want so you'll enjoy doing it.