It's been my experience that, things settle in a bit after a belt and timing-reset. Whether that's towards the advanced or retarded side is a crap-shoot. I've taken it upon myself to check timing again within a month or so after any process requiring the loosening and re-setting the tensioner/belt. Not a bad practice, even if not required by VW or Bentley.
I've got much experience playing w/timing, both static and dynamic (ECU) and have come to the conclusion, each engine has to be evaluated individually. I'm not sure any 'blanket' rules apply here. For instance, running your timing 'hot' statically (up around the green line) does seem to afford better cold starting and even mileage, but not in every case. Adapting your timing in VCDS definitely has an effect but only to the whole timing curve. It will also effect the total amount of dynamic advance available at the upper end. Running advanced timing by adapting it has the downside of over-advancing when cold starting. This manifests itself as the engine sounding more 'rattly' and generally courser running when cold. Looking at ScanGauge, I'm running 3-5 BTDC under those conditions compared to stock at 0-1 BTDC (or even slightly positive) when stock. The ECU is having a hard (or impossible) time meeting requested as well causing higher duty cycles.
Under stock conditions, the max advance you can get is somewhere around 16-18º where I can get 21º when advanced per the tuner's defaults (performance chip). The driving characteristics, however, change noticeably between the two on the average. Less advance (dynamically) results in lower power band and overall stronger feel in day to day driving. Hot advance results in more hollow mid-range response but, ultimately, slightly more go power under WOT conditions. Full advance makes for more rattly cold starts and higher PCP's as well but yield slightly better overall mileage also. For me, they're all a trade-off and one needs to experiment to find which they find most suitable. Setting your static timing to somewhere over the blue and before the green seems to offer the best starting as this is pre-ECU/dynamic and the closer to ideal you can set it, the better.
Think about your max timing required as retarding your static timing may limit your upper limit available. The pump (ALH) can only provide around 18º total advance and the more retarded you set it statically will dictate your max advance under WOT. For example, if I set my static advanced and advance my dynamic (adaptation) I can easily get 21º total. With everything pushed to the advanced side, however, it has a hard time meeting requested at idle. On the other hand, by setting my static lower and adapting my idle/start advance to around 0º (32768), I only get a total of around 18º. For mild to moderately modded ALH's... around 18º seems to be a good number. My car is well behaved set that way, though a bit muted on the top end and a bit less fuel efficient. I currently run about 19.5º total as it's a good compromise between all factors. For stronger city performance, I'll drop that to around 18º and gain some mid-range umph at the cost of high end performance and mileage.
Just my experience but I tend to look at the whole timing package as opposed to just the static portion. I don't think there's real 'magic' there. The static portion serves as a starting point for the dynamic and dictates the range available for the ECU/pump to work within. After that, the timing and related maps give the curve its shape within the limits of what the pump can do. There are ups and downs to each combination.
Any statements I made regarding timing adaptation should be considered risky and not taken lightly. Any changes are done at your own risk and I indemnify myself from any responsibility. As usual, YMMV...
