Why does the trade of pieces benefit the side with less space?

I have a very general question - why does trading off of pieces in the centre aid the side which has less of a space advantage? Here is an example to illustrate this point - I came across the following commentary about a certain position:

'' Black is happy with a massive exchange of pieces on e4; that’s the first thing to know. The trade of pieces would benefit black who has less space, therefore we (white) should avoid it and white has three reasonable options: 8.Ned2, which aims to recycle the knight via c4, the second option, 8.Neg5, puts some pressure on f7/e6. This would force black to make some concessions in his development. Third ... is 8.Ng3, which is the most popular and the preference at the highest level.''

     The player with less space will find it more difficult to develop as there less open squares and lines on their side of the board. They will also have trouble maneuvering to neutralize the opponent's threats and get counterplay. Trading a couple of pieces helps relieve the congestion.

if you trade off some of your opponent's strong pieces, then that frees up space for your own

There is a very good example of this made by GM Supi

With less space, it's ok to have fewer pieces.

Like in a bus, if you have some people, it's fine.

But when you have a huge amount of material to keep in a really closed space, it gets out of control, you need to open it up. Like a bus with an overflow of people

Thank you for your clear explanations!

By trading pieces when you have less space adventage you are getting rid of some of your opponents active pieces and you free up some squares they were controling with that piece. Also, later in the game you wont be cramped with your own pieces getting in your way.