Re: Power BI August 2026 Feature Summary

In our case we have very specific requirements due to the context of brand compliance, UI/UX consistency for commercial product etc.

However, if you're broadly 'open' to MS's (quite significant) changes to chart styles and functionality (plus slicers etc.) then yes, the ideal approach is to leave as much possible to the 'base theme' and only override the formatting you require to be bespoke, keeping your theme file as small and easy to manage as possible. This is also mentioned on the MS general (custom) theme page.

learn.microsoft.com/en-us/power-bi/create-reports/report-themes-create-custom (for some reason I can't post links so please add the usual 'https' if you want to visit it [or this may work by default, not sure])

This was the approach we took several years ago (back when navigators didn't exist and the default text box didn't even feature bullets!) when we first built our theme file, but since then we now have a detailed and well functioning UI/UX setup, so I've had to do the opposite and add multiple formatting values to better control the interface design. (Ironically though the 'new' donut chart inner radius now matches our original bespoke value of 70%.) Also, I've added multiple bespoke features using custom presets to facilitate custom icons and component-like bespoke formatting functionality etc., so for us there's no dialing it back at this point.

Anyway, the TL;DR is that yes, unless you require a specific set of formatting values and already have a well established 'custom' look and function in place, the path of least resistance is to leave as many default settings in place as you reasonably can, and only change/override the settings you need to.

Just bear in mind as MS makes changes with certain updates, you may see multiple changes to your reports depending on previous defaults being modified with certain releases, especially around areas like spacing, previous items that were switched off by default being switched on etc.