Do you subscribe to the notion that a pop up IFR clearance is acceptable to use on a consistent basis? Or does is show poor planning and use of the feature. Yesterday I had a crazy flight (to me) where the person I was flying with insists on flying everywhere VFR and then will pull out the pop up IFR request out of their back pocket when they need it. Even though they are a CFII. There were so many unnecessary headaches with it that I find it better and more prudent of me to plan and file on the ground. Especially in these spring/summer months when clouds pop up like this unwanted zit on my face.
Unnecessary headaches? Nope.
The suggestions here to first be receiving VFR advisories then requesting a popup when needed are routine and commonplace for both pilots, and the controllers granting them.... seamless is the correct term.
I would suggest not departing VFR into marginal weather, deliberately pointed into worsening weather with the full intent of asking for a popup. That's a little selfish, and not the intent of a popup.
If you're heading into a busy metropolitian area during push hours and the weather at your destination turns marginal (or worse), don't wait until being handed off to the ATC sector that's working aircraft approaching it. Pick it up earlier where the frequency likely to be much less busy.
It's been a long time since I was refused a popup (probably only once). Back in the 1980's, just outside of Class Bravo airspace (back then called a TCA). The busy controller instructed me to remain clear of the TCA, contact FSS (Flight Service), and air file. I did, and it was a real PITA. Learned a good lesson.
IMO, when the weather is beautiful VFR (end to end), unless you're a fairly new instrument rated pilot and need some practice or familiarity flying IFR in the system, don't file. I find VFR advisories in and around big cities provide shorter distances, a better choice of altitudes, and excellent traffic call-outs. Seems (to me) that ATC appreciates it.
A lot of GA pilots believe filing IFR and flying in clear and 100 is safer. I don't totally agree. More IFR flights contribute to ATC workload, making VFR Flight Following less effective.
Flying IFR at times is only providing separation from other IFR traffic. You still need to look out the windows.