César Azpilicueta's experience might mean a lot to Atletico Madrid, but at 33 years of age, of course, his quality is not as good as before and he can't play optimally anymore, but because the transfer fee is free, Atletico Madrid is a little lucky.
So far I haven't seen any significant movement in the Atletico Madrid team to improve their team to overshadow next season.
Atletico Madrid luck indeed from this signing as he is a free transfer player. 33 years old is still not too old and I think he will be a big hope for Atletico Madrid defense next season. Atletico Madrid did not make many changes in the transfer window because they identically used the existing squad for next season.
Teams from Laliga that often revamp their squad are Barcelona and Real Madrid because these two teams are far better financially than other teams. For Atletico Madrid, if they don't make big changes, they will likely continue to experience difficulties in the race for the Laliga trophy.
Currently, most of the Spanish clubs are suffering from finances which are hurting them badly, and they are not able to bring quality players just because of this having player like César Azpilicueta as free agent is good for the Atlético Madrid because now they are looking for the improvement as things are looking tough in next season while they will be competed with tough teams in Champions League and things are also not easy in La Liga even right now situation is also not good for the Real Madrid and Barcelona as suffering badly.
33 years old is good defender having long experience and quality will help them for improving their strength but still if they want to win title they have to give some intention for having improvement in their squad otherwise it's never been easy to stay at top level.