If you build the "evolution" (variation) into the style pattern, you're locked into always having the changes occur four measures in, eight measures in, etc. If it's a typical pop song with 8 bars, a 4-bar chorus, etc., that might work and save you a little button-pushing.

But most if not all of today's arrangers have four variations already built into the style. So you can play 4 bars, trigger variation 2, then var 3 for the chorus, back to var 2 for the second verse, var 4 for the bridge, etc.

One of the tips I read about style creation, is to build the most complex variation first, and then simplify it / thin it out for the simpler variations. If you create a pattern eight bars long for var 4, and truncate it to four bars for var 3, it will "wrap" and play through twice. If you truncate it to just two bars for var's 2 and 1, it will play through four times. This saves a lot of work!

I agree with your premise and wouldn't own an arranger without a style creator, unless I already had a way to make or convert custom styles for that brand.