It is a very interesting question and, as often, there is no universal answer: hence all the pleasure and interest of the modular synthesizer.
In my case, on about fifty modules, I use only 3 small modules strictly dedicated to effects: 2hp Verb, Pico DSP and Happy Nerding FX Aid (4hp version). I have to add the Monsoon (a Clouds clone with the Parasites firmware) reverb and the possibility to use sometimes the Disting mk4.
Why? Because I try to preserve as much as possible the nature, the transients and the texture of the sounds: the quality of the sound sources in a modular was from the beginning, and actually stays for me the main attraction next to the possibilities of CV of course...
So my most frequent use of effects remains the positioning in the mix, as one would use commonly a filter for example.
On the other hand, when I think of 'effect', I more often associate it with a deeper mutation of the sound such as the granularization of a Nebulae, or the metamorphosis by a Morphagene.
Pushing to the extreme, I would say that it is the whole modular that I conceive as a special effect for the sound: just like cinema is not theater and could even be viewed as a special effect versus the theater! (Think about Georges Méliès).
My philosophy of modular is not to try to reproduce what traditional synthesizers would do. In the same way that a sampler should not try to imitate an acoustic instrument just because it could.
'On ne devrait jamais quitter Montauban' (Fernand Naudin).