@JDBguest
Actually owning the seat with my nameplate on it does mean that my neighbor’s CANNOT sit there if I arrive late.
Our shul has signs in the lobby advising guests to check with an usher or the Gabbai for available seats. Also, a notice that seats with name plates are not available to be used at will.
I am seldom late, generally if caused by a true emergency. I expect my seat to be open when I arrive, The last time I was late was first Day R”H when my MIL was niftara the night before in our home. I took extra time to make sure my daughters had Mrs. CTL comforted and rounded up the grandchildren and arrived about 10. I found it comforting to have our family block of seats waiting for us.
That said, if I know I’ll not be in shul for Shabbos or Yuntif I let the Gabbai know in advance and he is free to let others use my seat.