Can you provide a source about that? Not trying to be difficult but all I can find is that it's not necessary because it's easily ignitable.

I found a couple of posts from another sight talking about this issue.

They wrote the following:
1) If you really really inquire of Accurate they will tell you that they do not recommend the use of fillers with 5744 because they have never tested their powder with fillers.

However, an answering post from the same sight wrote:
2)I had an email this afternoon from Accurate and they now say a filler is acceptable with XMP5744.

From Accurate's sight:

It can best be described as a fast burning Rifle or slow burning Magnum handgun double base “hybrid” powder, having the typical chemical composition of handgun powders i.e. 20% NG – and the geometry of a typical extruded single perforated rifle powder.

Rifle applications:

This makes the powder very ignitable, which makes it ideal for low loading density applications, such as reduced loads on bottle neck rifle calibers, and low performance “straight case” designs, such as the old “black powder” calibers i.e. 45-70 45-110 50-110 etc.

The powder is virtually insensitive to powder position, and there is no need for “fillers”. It will deliver consistent results at low performance levels. Although there will be some un-burnt powder (see paragraph below) the performance will remain consistent.

Due to its ignitability, any strength rifle primer can be used.