According to Elaine Gould, page 184 of Behind Bars (see screenshot), horizontal alignment (aka same vertical position) of tempo alteration markings is “helpful” but the most important thing is that “each marking is more or less a consistent height above the notation”.
When referring to horizontal alignment of dynamics on page 105, she says “whenever possible”.
So, from what I understand from her book, horizontal alignment of dynamics and/or tempo alteration markings are not mandatory according to Gould, but it can be considered good practice.
In my orchestral piece, my default parts sometimes have tempo alterations and tempo markings at many different heights above the notation in each system. It would be great to have a tool to either group them, or an alignment tool like in a software like Powerpoint that tells me when things are aligned.
