Both Dell monitors are 4K. Moving from the 27-inch U2725QE to the U3225QE’s 31.5-inch visible screen enlarges the desktop rather than adding pixels. At the same operating-system scaling, text, controls and windows become physically larger, but the amount of logical workspace stays the same. Reducing scaling fits more content while making the interface smaller again. This comparison applies to the two 4K Dell models; replacing a different-resolution 27-inch screen could also change the available workspace.
The larger screen adds about 10 cm of active width. For illustration, moving from the 27-inch panel at an eye-to-screen distance of 60 cm to the larger panel at 70 cm gives roughly the same horizontal span in your view. A shallow desk may leave little room for that extra distance, so the bigger panel spreads farther across your view when it stays close. Those distances illustrate geometry, rather than personal comfort thresholds.
The supplied stand is 189 mm deep on the U2725QE and 215 mm on the U3225QE. That footprint uses desk space; it does not tell you how far the panel sits from your eyes. The larger enclosure and base also leave fewer placement options when space is tight.
If a capable 27-inch monitor already works well close to your seat, keeping it avoids making the setup harder to place. The larger Dell has a clearer purpose when you want larger text at your preferred scaling and have room to accommodate its wider view.