2 external vs single ultrawide display

@bob_m10  Good questions to be asking when users are asking about this, since this is possibly a situation where you can end up giving users what they asked for, but not really what they wanted.  I'll address the questions below though:

The WD19 when paired with the XPS 13 9380 would have access to half of a DisplayPort 1.2 interface worth of bandwidth.  Dell's documentation says this is enough to run a single display up to 2560x1440 or 4K but only at 30 Hz rather than the standard 60 Hz.  Ultrawide resolutions aren't accounted for in Dell's documentation, and 3440x1440 falls between those resolutions.  So looking at the math, 2560x1440 requires 5.6 Gbps of bandwidth.  3440x1440 is 34% more pixel area, so it should require about 7.5 Gbps of bandwidth.  Half of a DP 1.2 interface, which is what the WD19 will have available from an XPS 13 9380, offers 8.6 Gbps of usable bandwidth.  So the math says it will work.  But just to be clear, I have not actually tested that.  If it doesn't, you'd need to get a Thunderbolt 3 dock like the WD19TB, which when paired with your system would tap into 4x more bandwidth than the regular WD19.  But yes, the Intel GPU itself definitely supports 3440x1440 resolution because it supports displays up to 4K.

In terms of maximizing windows, you're exactly right, and that's a big reason I prefer two separate displays.  (Another is because that allows a lot more freedom in terms of how you physically arrange the displays, i.e. having them in a V arrangement or having one "dead-on" while another is angled inward toward you.  An ultrawide doesn't allow that.)  I greatly prefer being able to quickly maximize two applications on two separate displays, or to use Windows Aero Snap to quickly put 4 applications up, each taking up half of one display.  I also find that having separate displays helps me mentally compartmentalize.  Ultrawides aren't as useful there.  Dell has a utility called Dell Display Manager that can be used to carve up ANY display in a variety of ways to help with this, but I've never used it.  But shortcuts like Aero Snap such as WinKey+Left/Right to quickly resize an application window to occupy the left or right half of your display become less useful.  The main use cases I see for ultrawides are scenarios where having one huge interrupted canvas really is a benefit, such as video editing where you have long timelines or of course gaming.

In terms of pixel area, dual 1080p is actually less total workspace.  1920x1080x2 = 4,147,200 pixels.  3440x1440x1 = 4,953,600 pixels.  So the ultrawide gives you almost 20% more total space.  But whether that space amounts to more utility is a separate question.  The ultrawide gives you more vertical real estate (1440 pixels vs 1080), but less horizontal real estate (3440 vs. 3840 total).  Stated differently, dual 1080p results in a total aspect ratio of 32:9, whereas the ultrawide is 21:9.

The ultimate ultrawide in my opinion is a 32:9 aspect ratio display, such as the Dell U4919DW.  That is a 5120x1440 display, so it is two 27" 2560x1440 displays fused together as a single canvas.  Some people use that display to display two completely different PCs side-by-side, since in that case each source system gets a 27" 1440p display to itself.  But that display is of course quite a bit larger and more expensive than what you're looking at, and you would definitely need a Thunderbolt 3 dock to run it.  But if you had it, the XPS 13 9380 would run it.