If you did actually a small search on Google, you would find some good results and explanation !

I can say briefly, de alone with no definite article is used usually when we speak about a very GENERAL concept, just like:

• Un homme de principe/science/guerre

but when we know definitely what we are talking about, the definites articles should be added, just like:

• Le bruit de la ville

here we don’t intend to say or generalize the concept of noise bruit to all cities.However, only a specific city that we mention.

As for most languages, the french language practice obeys some rules. One of these rules is called "règle de l’article contracté". It states that when "une préposition" is followed by "un article défini", the result should be "un article contracté" (contracted article).

In the case of:

une compression du personnel

"du" is here the contracted article of "de le" which respectively are "préposition + article défini". Consequently, it is incorrect to say:

une compression de le personnel

The use of "de" / "du" depends on whether "personnel" is definite or not. In our case, it isn’t so one must use "du".

If "personnel" is definite, "de" should be used as in:

une compression de personnel de la comptabilité.

Note that "de la" of "de la comptabilité" is not concerned by the rule in question since it is "du genre féminin" (feminine gender).