A network of (“thousands of”) servers has — like most things — pros and cons.

Some of the pros are:

• The network is more resiliant against outages. If lemmy.ml is down, all other users can still access the network.
• It's hard to take legal action against the network or to buy it out (like Big Players™ like to do to get rid of potential competitors).
• It allows various similar or even conflicting moderation policies. The network, i.e. the infrastructure doesn't allow or prohibit any specific opinion (the communities do).
• It allows for different ways to pay the bills: goodwill of the admin, donaitions, ads, fee or selfhosting. The latter also allows great control over the data so you control your privacy.

Some of the cons are:

• Content is replicated across servers, which increases the total amount of data stored.
• Latency and speed suffer.
• Interoperability with the wider Fediverse is less than 100%, which can create confusion and frustration.
• Discovery is more difficult.