The SSPX used to have a policy of never leaving a priest in place more than 2-3 years, how often that is enforced waxes and wanes. A few times they have left a priest in place 5,8 even 10 years and the results have not been good. I understand how the transfer of a beloved priest can be hard for both priest and parishioners but when a 'cult of personality' arises around a single priest it is not a good thing. I have seen this happen personally, a parish will become more attached to a particular priest than they are to the Faith itself. The priest's word and opinion becomes gospel instead of him being a messenger of the Gospel. Even a good and humble priest can become proud and vain in a situation where he is put on a pedastal. This is also why priests must live in a priory and not out on their own.