How important is a Mokom Kavouah for Tefilla on a daily basis in the same Minyan (time wise) when a non member of the Shul - in a Shul where by the rules of membership there are non fixed seats but de-facto there are, always takes a seat that he knows and has been told is a Mokom Kavouah for a member of the Shul. That member feels that the lack of this availability to him has affected his Parnossoh and other issues in life
Shalom, You are correct that it is important to pray in the same place on a regular basis - makom kavu'ah. The source for this is from the Talmud (Berachot 6b) where it says that the G-d of Avraham will help everyone who fixes a set place for their prayers. This is learnt out from the verse in Bereishit (chapter 19) where it states that Avraham went to the place he had stood in - indicating that he had a set place for prayer. This law can be found in the Shulchan Aruch (90,19). However the boundaries of this law are not as strict as one might think. First of all, the definition of a set place is within 4 cubits of one's seat. This is approximately 2 meters in any direction, which includes a lot of seats one could sit in and still be in their makom kavu'ah. Secondly, even when one cannot use their set place (or up to 4 cubits around it), one is allowed to move from there for a good reason, or if one is forced to. It seems that the case you are talking about would certainly come under this rule. Also, giving up one's place for a mitzvah is also considered as permissible (see the Tur ibid) - and bringing peace between congregants is certainly a big mitzvah! So, it seems that in this case, the person who lost the chance to sit in their set place still fulfilled the halacha - either because they sat within 4 cubits of their place, which itself is considered as the set place; or because they moved from their place for a good reason, a mitzvah, or because they were forced to. In all these cases, when a person did not pray in their set place because they followed the directives of the halacha, certainly no evil will befall them. It seems from your question that there may be some tension or even, G-d forbid, bad feelings and anger amongst those praying in your minyan. This could affect how a person's prayers are accepted, and blessings of livelihood etc (though I don't claim to know the cause of one's troubles - and may Hashem send only blessings and good tidings). May I suggest that both parties who want to sit in the same seat try to make peace, and if needs be, go amicably to the Rabbi of the minyan for his ruling. The benefits of peace and love amongst the Jewish people certainly are much greater than the benefits of praying in a set place. Blessings.