There is an application note AN5067 which details how accurate you can expect the HSI to be.
They especially mention, that after a reflow process (or any soldering process) there will be a drift, which can be as big as 2.5 % - and they consider it still being within the expected range (not inside the specification).
The drift usually happens in a way that the end frequency will be lower than the specified value.
So depending on the end product specification it might be worth testing how much the assembled unit differs from the specification to see if it needs additional trimming.
The new variants with MSI also offer the possibility to automatically trim the MSI to an external 32 kHz oscillator, which results in a quite precise clock even over temperature with a very low increase in power consumption. But of course with additional cost.