Everyone's use case is different, but I've been testing memory pressure since first day as I'm very curious. Internally got just the base 16GB. Haven't seen the machine go over 14GB. To give an example, tonight I had the following apps open and processes running:
13 safari tabs open (13 different websites), Apple Maps, Calendar, Microsoft Excel, iMsgs, Music, TV+, YouTube playing a video, Apple News, LR Classic, Disk Utility, Airport Utility, Calculator, Email, and whatever Mac/OS runs in the background.
Max memory pressure was ~13.5GB, always in the green. No slowdowns noticed anywhere on the machine. In addition I had my Time Capsule backup disk in the midst of a big data exchange with my external disk. Also running dual screen; ASD as Main, old Apple Thunderbolt Display as extended.
The machine that I upgraded from is a 2017 iMac i7 with 32 GB RAM and a 3TB Fusion Drive. The M4 base blows that out of the water. Mac O/S is a master at memory Mgmt with their M SoC. In my workflow I rarely have all those processes open all at once. Don't do video, most intense thing I do is large amounts of Lightroom edits. So still a lot to test but initial reaction is one of amazement. I figured I would return this within days. Now thinking very seriously about keeping it.