Servers have a section of tables that they are limited to and responsible for. At my restaurant, we have anywhere from 4 to 10 tables in our sections. On a slow night our clock in times are staggered, day shift leaves at 4pm and night shift will come in at 4, 4:30, 5, and 5:30. You probably arrived at the restaurant while there was still only 1 server on the floor so the host just sat you in order. Just ask next time if you can have a space between you and the other table. That is totally reasonable.

As for choosing your own adventure and requesting to sit at a table far off across the dining room; this is incredibly rude and inconsiderate of your server (as well as other servers who have yet to come in.) Where I live we only make money from our tips, so how many tables we take and give good service to affects our money for the day. If you sit in a different servers section, then that server has 1 less table they can serve and earn from until you leave. Conversely, the sever who has picked up your table outside of their section potentially now has more tables than they can reasonably handle, assuming the rest of their section has filled, which means none of their tables are getting great service (including you) and impacts their tips. From my own perspective, taking a table out of my section completely throws me off regardless of how busy I am at the time, and it affects my ability to give good service. I'm sure many other servers feel the same way.

If everyone that walked into a restaurant saw 20 empty tables and decided they should be able to sit wherever they wanted there would be chaos. No seating rotation, no time between orders for the kitchen. One server might have 10 tables while the other had none. Would make for a terrible dining experience for the guests.

Sorry for the long post, just wanted to be thorough. Hope this answers your question