Is a distribution panel necessary when pre-wiring for internet and cable TV?
Can't speak as much to the TV part, though an awful lot of TVs now work with internet connections. But as far as the internet connection, my recommendation is to wire up CAT 5e (or better) everywhere. Each cable should have one end in the desired location and the other end on a patch panel like:

Then you use cheap patch cables to connect to your switch or router. You mention DSL - that may be the technology now, but in the future it may fiber or Starlink. But you can change that easily enough.
The &quot;main box&quot;, which can be a modem or a router or a combination of the two (typically with residential installations it is a combination modem/router/WiFi access point) may be placed where you put your patch panel but may be someplace else. A lot depends on the particular company, whether they do a professional installation or a &quot;self install&quot;, the design of your house and other factors. In particular, if you have WiFi as part of the installation then you don't want the WiFi next to the patch panel in the basement or garage, etc. - you want your WiFi access point in a central location. Sometimes that means putting the router/WiFi in a better location and connecting it through one of your wired access points down to the patch panel and just putting a simple switch next to the patch panel. Sometimes the best solution is to put the router next to the patch panel and install a separate WiFi access point in another room. Sometimes multiple WiFi access points are needed for good coverage.
Speaking of good coverage, the best WiFi coverage is often obtained by putting WiFi access points in the ceiling, using Power over Ethernet to provide power and signal through one cable, so you may want to consider prewiring some ceiling locations as well.
What you can't change easily are the actual cables in the wall. Conduit really is a good idea. Think about all the people who had CAT 3 (or worse) cables and now really need CAT 5 in order to have a fast network. Or all the people who had coax and now want CAT 5 for their TV. Your house will (hopefully) be around for a long time, but nobody knows what will be popular for connections 20 years from now. It could easily be fiber everywhere, or some future CAT 'n' - all easy to install if you have conduit, very hard without.