The answer to this is not one or the other...the answer is:

You and your partner must have the same *values* with regard to self-change/self-growth, and must both value these to the same extent or magnitude.

In other words...if you and your partner BOTH highly value self-growth/self-improvement (to the same degree), then you will both encourage each other with the same degree of reciprocity...it will feel good to encourage your partner, and you will also be emotionally charged by your partner's encouragement.

Likewise, if you and your partner more highly value constancy, stability, etc., then you will both be satisfied with the degree to which (of lack of degree to which) change in the other is encouraged.

It is a lack of reciprocity of value systems that creates tension within a relationship. If one values "change/growth" while the other values "stability/constancy"...there will be tension, and vice versa. This creates all kinds of resentments, feelings of inadequacy, etc. Ideally, you'd like to be equally matched with regard to where your values are placed and the extent to which that thing is valued.

Hope that made sense :P